International Standards Is Normally Carried out Through ISO Technical Comtnizzees

INTERNATIONAL ISO STANDARD 898-2

Second edition 1992-11-01

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Mechanical properties of fasteners - Part 2: Nuts with specified proof load values - Coarse thread

Caract&-istiques rmkxniqrres des t%ments de fixatim -- Partie 2: Eo-aus avec charges d’i+renve specifi6es - Filetages 2 pas CJI-OS

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Refcrence numbcr

.- -- ISO 898-2: 19921 E) _ _. ^ -- _ _ _. _ ___ :------= ISO 898-2:1992(E)

Fsreword

ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO metnber bodies). The work of preparing International Standards is normally carried out through ISO technical comtniZZees. Esch tnember body interested in a subjed: for which a technicat commitlee has been established has Zhe right 90 be represented on that cotnmittee. International organizations, govern- mental and non-govet-nmental, in liaison with ISO, also take part in the work. lS0 cotlaborates ctosely with the International Electrotechnical Commission (IEC) on alt mattet-s of etectrotechnicat standardization.

Draft lntet-national Standards adapted by Iahe techllical cotm-nittees at-e circutated to the member bedies for voting. Publication as an tnter- nationat Standard r-equires approvat by at least 75 94 of the member bodies casting a vote.

International Standard ISO 898-2 was prepared by Technical Committee ISO/TC 2, Fasfeners, Sub-Committee SC 1, Mechanicai properfies of Tasfeners.

This second edition cancels and replaces the fit-st edition (ISO 898-2:1980), which has been technicalty revised.

ISO 898 consists of ,the fotlowinq . parls, under the general titte MecI~a1)- ical proper-fies of I;r--asfeners:

_I Part 1: Belts, screws arM studs

-- Part 2; Nufs wifh specified proof Load values -- Coarse fhread

- Part 5: Set screws and similar threaded fasteriers not- under t ensile siresses

- Part 6: Abts with specilred proof Load vahes - Fine pifch thread

- Part 7: Torsioriai fest ai ld minimum torques for bolts and screws with nominal dianiete/-s I mm to 10 mm

Annexes A and B of Ibis pst-t of ISO 898 are for infortnation only.

0 ISO 1992 All rights reserved. No part of this publication may be t-cproduced or utilized in any form or by any means, electt onic or mechanical, i~~cluding photocopying and microfiltn, without permission in writing from the publisiter-. Internalional Orgat~ization for Standard ization Case Postale 56 * CH-1211 Genkve 20 * Switzer land Pr inteci in Switzerlatid

ii INTERNATIONAL STANDARD ISO 898-2:1992(E)

MechanicaII properties of fasteners -

Part 2: NUSSwith specified proof load values - Coarse thread

1 Scope --- corrosion resistance (see ISO 3506);

This international Standard specifies the mechanicai - ability to withstand temperatures a bove properties of nuts with specified proof Load values --t--300 OC or below - 50 OC. when tcsted at room temperature (sce ISO 1). Prop- NOTES erties will Var-y at higher and lower temperature. 1 Nuts made from free-cutting steel should not be used It applies to nuts above -+ 250 “C. -- with nominai Ihrcad diameters up to and incIud- 2 For special products such as nuts for high-strength i ng 39 mm; structural bolting, and overtapped nuts for use with hot- dipped galvanized boits, see the product Standards for - of trianguIar ISO thread and with diameters and appropriate values. pitches according . to ISO 68 and ISO 262 (coarse thread); 3 For assemhlies with threads having tolerantes wider than 6H/6g, there is an increased risk of stripping; see also table 1. -- with diameter/pifch combinations according to ISO 261 (coarse thread); 4 In the case of thread tolerantes other or larger than 6t-1, a decrease of the stripping strength should be con- --- with thread tolerantes 6H according to ISO 965-1 sidered (see table 1). and ISO 965-2;

-- with specific mechanical reguirements; Table 1 - Reduction in thread strength I_ with widths across flats as specified in ISO 272 Test load, 74 or equivalenl; Thread Thread tolerantes - with nominal heights greater than or equal to greater less than or O,W*‘; than equal to 6H 7H 6G

- made of carbon steel or low alloy steel. -_ M2,5 100 -- 95,5 .-- 1.--.- It does not appfy to nuts requiring special properties such as

-- lackirig abiliiies (sec ISO 2320);

--- weldability;

‘) 1) is the nominal diameter of the internal thread in accordance with ISO 724. ISO 898-2:1992(E)

2 Normative references ISO 6507-1: 1982, Mefallic n-,aterials ---- Hardness test - Vickers test -- Part 1: HV 5 to 1-N 100. The foIiowing Standards contain provisions which, through reference in this text, constitute provisions ISO 6508:1986, Metallic rnaterials -- Hardness fest -- of this par-t af ISO 898, At the tirne of publicaiion, the Rockwell fest (scales A - 8 - C - D - E - F - G - H - editions indicated were valid. All Standards are 0 subject to revision, and Parties to agreements based on this part of 1SO 898 are encouraged to investigate the possibility of applying the most recent editions of the Standards indicated below. Members of IEC 3 Designation System and ISO maintain registers of currently valid Inter- national Standards.

ISO 1:1975, Siandard refereuce iemperafrrre for in- 3.1 Nuts with nominal heights > 0,811 dustrial length measrIrernerIts. (effective lengths af thread > 0,6/))

ISO 68:1973, ISO general /lur/lose screw fhreads - Nuts with nominal heights > 0,811 (effective lenqths Basic Profile. of thread > 0,6D) are designated by a nur-&& to indicate the maximum appropriate pt-operty class of ISO 261:1973, ISO qeneral purpose metric screw bolts with which they may be mated. fhreads - General i/an. Failure of threaded fasteners due to over-tightening ISO 262:1973, ISO general purpose metric screw tan occur by bolt shank fracture or by stt-ipping of threads -- Seiected sizes for screws, bolts and nuts. the threads of the nut and/or bolt. Shank fracture is sudden and therefore easily noticed. Stripping is 1SO 272:1982, FasteIlers - Hexagon prodlrcts -- gradual and therefore difficult to detect and this in- Widths across flats. troduces the danger of partly failed fasteners being left in assemblies. ISO 286-2:1988, ISO System of Limits and fits - lt would therefore be desirable to design thr-eaded Part 2: 7ables of Standard tolerante grades and limit connections so that their mode of failure would al- deviations for holes and shafls. ’ ways be by shank fracture but, unfortunateIy, be- Cause of the many variables which govern stripping ISO 724:1978, ISO mefric screw threads - Basic di- strength (nut and bolt mate+! r,trzngths, thread mensions. clearances, across-flats dimensions, etc.), 11uts would have to be objectionably thick to guarantee ISO 965-1:1980, ISO general purpose metric screw this mode in atl cases. threads -- Polerances --- Part 1; Frinciples and basic data. A bolt or screw of thread M5 to M39 assembled with a nut of the appropriate propet-ty class, in accord- 1SO 965-2:1980, ISO yeneral purpose tnetric screw ancc with tabte 2, is intended to provide an as- threads ---. Tolerallces - Parf 2: Limits of sizes for sembly capable of beirigg tightened to the holt proof generai purpose holt and nuf thr,eads -- Mediwn load without thread stripping occurring. quality. However, should tiqhtening beyond bolt proof load ISO 4964: 1984, Steel -- Hardness conversious. take place, the nut‘design is intended to ensure at least IO % of the over-tiqhtened asscmblies fail ISO 6157-2:--- l) , Fasteners --- Surface discontincrities through bolt breakage in Order to warn the User that - Part 2r Nuts with threads MIS to M39. the installation practice is not appropriate.

ISO 6506: 1981, Mefallic rnaterials - Hardrjess test -- NOTE 5 For more detailed information on the strength Brinell test. of screw thrcad assemblies, see annex A.

1) 7-o be published.

2 ISO 898=2:1992(E)

Table 3 - Designation System and Stresses under Table 2 - Designation System for nuts with nominal proof load for nuts with nominal heights 2 0,5D but heights > 0,811 < 0,8D 9 Mating bolts Nominal stress Actual stress Property Property class of under proof load under proof load nut class of Nimm* N/mm* nut Property cfass Thread ranges 04 400 380 -- ---~------_---, - -- 4 3.6: 4.6; 4.8 > M16 >- M 16 05 500 500 -- ---_----. -_-_---.. ------.~-.------~-- 3.6; 4.6; 4.0 <; M16

5 .------_I-- .~XII___ < M39 .-.- 5.6; 5.0 < M39

.-_-.__I_ ------. ---- -~-._---- 6 6.8 < M39 < M39 ------_------.--_-.--c- ----.-- .------.-.-----___-._-----~ 4 Materials 8 8.8 Nuts shall be made of steel conforming to the ---- Chemical composition limits specified in table 4. 9 _--_-_ 10 Table 4 - Limits of Chemical composition ------__ Chemical cotnposition litnits 12 ------. Property ctass N 0-T‘F .. In yeneral, nuts of a higher- property class tan t-e- place nuts of a Iower property class. This is advisable for a bolt/nut assernbly going it-tto a stress hicj-Ier than the yield st.ress or the stress under proof load.

___---~._- --- ~_ -_ ____^ je 2) ; 05 i, j 0,58 j 0,30 / O&+iii-- 3.2 Nuts with ncxr~inal heights > 0,511 hut < 0,811 (effective heights of thread > 0,W but

< 0,611) I I I 1) Nuts of these proper-ty classes may be manufactured Nuts with nominal heiqhts 2 0,51) but c 0,811 (effec- from ft’ee-cuttiny steel unless otherwise agreed between the tive height of thread 5 0,4D but c 0,6/1) are desig- purchaser and the tnanufacturet-. In such cases, the following maximutn Sulfur, phosphorus and Icad contents at-e per- nated by a combination of two numbers: the second rnissible: itrdicalcs the nominal stress under proof load on a hardened test mandrei, while the fit-st inclicates that sulfur 0,34 74; phosphorus 0,ll %; Iead 0,35 %. the loadability of a bolt-nut assembly is reduced in 2) Alloying elements may be added, if necessary, to de- comparison with the loadability on a hardened test velop the mechanical properties of the nuts. mandrel and also in cotnparison with a bolt-nut assembly described in 3.1. The effective loading ca- pacity is not only detcrmincd by the hardness of the Nuts of property classes 05, 8 (style 1 above M16), nut and the effective height of thread but also by the 10 and 12 shall be hardened and tempered. tensile strength of the holt with which the nut is assembled. Table 3 gives the designation System and the Stresses under proof Ioad of the nuts. Proof loads arc shown in table 6. A guide fot- minimum 5 Mechanical properties expected stripping strengths of the joints when these nuts arc assembled wif.h bolts of vat-ious When tested by the methods described in clause 8, ihe nuts shall have the mechanical properties set property classes is shown in table 7. out in table 5. Tahle 5 - Mechanical properties

Propefty class 04 05 4

I I 1 , T t 1 Thread j S tress Stress ! Stress 1 under Vickers / Vickers I under Vickers : proof hardness Nut lI hardness Nut proof hardness Nut :1 ioad HV load I-W Load HV f 1 % 5 i 1 1 i 1 1 1 iess 1 l I I i greater 1 than or [ i l j I I than j eaual to I N/mm2 min. max. state style i N/mm2 i .mm. max. / state style 1 N/mm2 ,min. / max. state style l I 1 l F , I Ir i 1 / I I I l 1 I 1 I 1 i l l 1 I l t i / I 1 I I 1 i l l I i1 I I I I j - - 4 1 I PA7 Nil0 1 380 188 302 i NQTif i thin ’ 500 j 272 ’ 353 ,i QT2) (! thin / I i 1 i 9 1 I I l-l- 1 - 1 I i I j 1 i ! I 1 t I I I 117 1 302 j NQT:j j 1 I j

f Property class 5 3) 5 8 i ?- T 7 ; 1 1 t T Stress Stress I Stress Stress Thread i 1 1 i under I Vickers under Vickers / under Vickers l under Vickers 1 I proof l hardness Nut proof hardness / Nut proof hardness 1 Nut proof hardness Nut load HV load HV 1 Joad I-W Load i-iV ! 1 j % sP % % l l I less I / i I greater ’ than or I Nimm2 min. , max. state i style Nt’mm2 N/mm2 min. max. state styl e than equal to N/mm2 min. max. state ! j 1 ! / / 1 I t t -- i I t 520 300 i- 1 - / M4 i / / 1 l 1 1 t i ~4 i M7 580 --r l 855 i I j 130 l !50 ij 1 - I J 1 302 NQTA) 680 / 202 NQ1 ‘11 1 1 l- 370 IM7 / MIO T 530 1 1 I ( i I l l I1 I i 1 MIO 1 f 610 höö- L t 880 l 1 1 L / + l i 1 i //Y-+i- 630 t 720 170 1 i 1 233 353 j Q-l-2) j 180 1 302 1 NQTU i 2 1 i r I I Ll / I I L 1 ! 1 1 Property class i 9 10 12 l *- T T ?- 1 Thread l Stress Stress i Stress TStress / f under Vi ckers under Vickers j under Vickers under Vickers hardness Nut proof 1 hardness Nut proof hardness Nut proof / hardness Nut HV ’ Load I-W load HV I Load HV <1, SF -& % ~ 1 I l l i i 1 1 i j l/ min. max. state style N/mm2 min. max. ’ state style Nlmm2 min. ’1 max. ’ state style N/mm2 i min. max. state style ’ i 1 I l I I i c I t 7- 170 1 040 1 140 I t 1 150 i / 1 l- 1 1 040 1 140 l 1 1 150 I I 2% 1 353 1 cy-21 1 ! i I i c 4 302 NQTI j 2 1 040 272 353 GT?) i 1 1 140 1 1 160 272 353 QT2) 3 188 I 1 I / 1 I I- : M-l0 M16 ’ 950 1 050 1 170 i ! 1 190 I ! I 1 I I l 4 l f Ml6 IM39 j 920 1 060 - - 1-1 - - 1 200 l i i l 1 A 1 I / i i 1 1) NQT = Not quenched or tempered. --l / 2) QT = Quenched and tempered. 3) The maximum bolt hardness of property classes 5.6 and 5.8 will be changed to be 220 HV it: the next revision of ISO 838-1: 1988. This is the maximum bolt hardness in the thread engagement area I whereas only the thread end or the head may have a maxlmum hardness of 250 HV. Therefore the values of stress under proof load are based on a maximum holt hardness of 220 HV. I NOTE - Minimum hardness is mandatory only for heat-treated nuts and nuts too iarge to be proof-!oad tested. For all other nuts, minimum hardness is not mandatory but is provided for guidance only. For nuts which are not hardened and tempered, and which satisfy the proof-load test, minimum t ardness shall not Se Cause for rejection.

Yable 6 - Proof Load values - Coarse thread l ti j 1 1 l , Property cfass 1 Thread I Nominaiof the stressmandrei area 04 ! 05 1j! 4 j 5 : 6 8 9 / Kl 1 12 i I pitch ] 4 I Thread 1 ;* S i I Proof ioad (A, x Sp) / / l 1I IN I I I 1 i/ mm I mm* l / 1’ style 1 i! style 1 1 style 1 style 1 i style 2 f siyle 2 ] style 1 j style 1 style 2 1 I I I I l 1 M3 i 0!5 $33 1910 1 2500 j - j 2600 i 3 000 4 000 - ’ 4 500 5 200 1 5700 5 800 i I M3,5 i 061 6J8 1 2530 l 3400 ; - / 3550 j 4050 5400 - ] 6 100 j 7050 i 7 700 7 ao0 l rd4 ;j 02 0,75 j334oi44ooj - / 4550 5 250 7000 ' - 7 900 ; 9 150 i 10 000 IO 100 l j l 0 I 1 i l l I M5 j 0,8 f ?4:2 I 5400 Il 7 100 1 - 1 8 250 i 9 500 :2 740 1 - 1 i3000 / 14 ao0 ! 16 200 1 I l M6 / 1 20,l I 7640 / 10000 / - , 11 700 j 13500 17 200 / - ia 400 1 20 900 ! 22900 ! ' 1 M7 i 1 28:9 1 11 000 1 14500 - 1 ?6800 1 19300 24700 - 26400 30 100 1 32900 / / / 1 ! ! 1 i M8 i 1,25 1 36,6 13 900 i 18300 / - 21 600 1 24 900 31 800 - 34400 1 38 100 / 41 700 42 500 NI10 ! 195 58 / 22 000 / 29 000 - ; 34200 / 39400 50500 - 54 500 60 300 1 66100 67 300 IA12 it IJ5 84,3 32 000 1 d2 200 f - j 51400 / 59000 100 300 l i 74 200 ! - I/ ao 100 88 500 j/ g8 6oo l 1 I t i I I M14 ! 2 115 43700 i 57500 - 70 200 80 500 SO1 200 - i 109 300 ' 120800 ?34 600 136 900 M16 1 2 757 138 200 - 149 200 1 164 900 j 183700 186 ao0 Ul18 j 2,5 192 176 600 1 170 300 1 +l76 600 203500 1 - 230 400 I 1 1 I i i l M20 2,5 245 225 400 218 100 t 225400 259700 - 294 000 M22 2,5 303 278 800 1 269 700 l 278 800 / 321 200 1 - 363 600 l IW24 ' 3 353 324 800 314 200 324 800 374 200 - 423 600 I j 1 M27 j 3 459 422 300 408 500 422 300 , 486500 - 550 800 i I M30 i 3,5 1 561 516 100 1 499300 516100 594700 , - 673 200 M33 375 l 694 638 500 / 617 700 638 500 735600 - 832 800 l 1 M36 4 817 310500 i1 308 500 / 416 700 / 514 i700 / 588 200 751 600 727 100 751 600 ' 866 000 - 980 400 M39 4 976 370900 / 488 000 1 497 800 1 614 900 / 702 700 897 900 868 600 897 900 1 035 000 I - 1 171 000 I I f j ISO 898-2: 1992(E)

7 Failure loads for nuts with nominal shall be the last quarter- of the Gg range on the height > 0,50 but < 0,8D minimum material side.

The vaiues of failure loads given in table 7 for guid- ante apply to different bolt classes. Bott stripping is the expected failure mode for lower strenqth bolts, while nut stripping tan be expected for’ bolts of higher property classes.

Table 7 - Minimum bolt stress when stripping -- occurs Proof load Miniitrum stress in the core of holt when stripping occurs Property stress of the class of nut PJ/mm* the nut N /mm* dh= d DU”

04 380 ~------_ -~--- 05 500

8 Test methods

8.1 Proof load test

"1 Dll is takon from tSO~2. The proof load test shall be used wherever the ca- pacity of available testing equipment permits, and shall be the referee method for sizes > M5. Figure 1 - Axial tensile test

The nut shall be assembled on a hardened and threaded tesl mandrel as shown in figures 1 and 2. For referee purposes, the axial tensile test is decis- Load ive. t The proof load shall be applied against the nut in an axial direction, and shall be held for 15 s. The nut shall resist the load without failure by stripping or rupture, and shall be removable by the fingers after the load is released. lf the thread of the mandrel is Har damaged during the test, the test should be dis- carded. (lt may be necessary to use a manual _..._ wrench to Start the nut in motion. Such wrenching is 35 permissible provided that it is restricted to one half n turn and that the nut is then removable by the fin- -c gers.) i----- The hardness of the test mandrel shall be 45 tiRC minimum-

Mandrels used shall be threaded to tolerante class 5h6g except that the tolerante of the major diameter Figure 2 - Axial compressive test

8 ISO 898-2:1992(E)

8.2 Hardness test The RockweIt hardness test shall be carried out in accordance with the requirernents of ISO 6508. For t-outine inspection, hardness tests shall be carried out on one bearing surface of the nut and the 8.3 Surface integrity test hardness shall be taken as the mean of three values spaced 121Y apart. In case of dispute, the hardness For the surface integrity test, see ISO 6157-2. tests shali be carried out on a longitudinal section through the nut axis and with impressions placed as 9 Marking close as possible to the nominal major diameter of the nut thread. 9.1 Symbols The Vickers hardness test is the referee test, and Marking sytnbols are shown in tables 8 and 9. where practicabte a Load of HV 30 shall be applied. if Brineil and Rockweil hardness tests at-e appiied, 9.2 ldentification the conversion tables in accordance with ISO 4964 shall be used. Hexagon nuts of threads > M5 and all property classes shall be marked in accordance with the The Vickers hardness test shall be Garried out in designation System described in clause 3, by in- accordance wi1.h the requirements of ISO 6507-1. denting on the side or bearing surface, or by embossing on the chamfer. See figures 3 and 4. The Brinell hardness test shall be carried out in ac- Embossed marks shall not protrude beyond the cot-dance with the rcquit-ements of ISO 6506. bearing surface of the nut.

Marking dot my he replaced by mmufai;tr~rer’s mark here

Figure 3 - Exampies of marking with designation Figure 4 - Examples of marking with code Symbol Symbol (clock-face System) Table 8 - Marking symbols for nuts with property classes in accordance with 3.1 T T 4 I 6 8 9 IO 12”) I $ t8 i 4 1 6 8 9 10 12 l 1 l .-c j- t I e 1 l : 2 / l ! 1 1 .Iz or Code symbol i l I jciock-face System j 1 2 1 83 l ij i / / 1 L L i “) The marking dot cannot be replaced by the manuiacturer’s mark. /

Tabie 9 - iWarking for nuts with properQ classes in accordance with 3.2

Propefty class

Marking ISO 898-2:1992(E)

9.3 Marking of left-hand thread

Nuts with ieft-hand thread shall be marked as shown in figure 5 on one beat-ing surface of the nut by in- denting.

1) s - width across fjats.

Figure 6 - Alternative left-hand thread marking

9.4 Alternative marking

Alternative or optional permittcd marking as stated Figure 5 - Left-band thread marking in 9.1 to 9.3 is left to the choice of the manufacturer.

9.5 Trade (identification) marking

The trade (identification) marking of the manufacturer is mandatory on all products covered by the Marking is reguired for nuts with threads > MS. obligatory marking requirements for property classes, provided this is possible for technical rea- The alternslive marking for Iefl-hand thread shown sons. Packages, however, shall be marked in all in figure6 may also he used. cases.

11 ISO 898-2:1992(E)

Annex A (informative)

Loadabiiity of boltkd connections

(Explanatory note concerning the specifications of Technical Committee ISO/TC 2 reaardina nut strength and nut design-) %J J

Following the introduction of the ISO Recommen- Following publication of both ISO Recommen- dation on property classes for bolts and screws dations, this System of property classes has been (lSO/R 898~1:1968), an ISO Recommendation on introduced worldwide and has proved to be a suc- property classes for nuts (ISO/R 898-2) was pub- cess. lished in 1969. These ISO Recommendations to- gether produced a new System for the property In 1973 the Sub-Comtnittee SC 1 of lSO/TC 2 com- classes of bolts, screws and nuts, and, in conjunc- menced revision of the BO Recommendations on tion with new rnarking requit-ements, provided a the basis of experience gathered and also planned clear Statement of the loadability of a bolt-nut as- to convert both Recommendations into ISO Stan- setnbly. dards. In 1974, a draft lSO/DlS 898-1 on property classes for bolts and screws was pubiished, incor- a) In the case of bolts and screws, the symbol indi- porating certain modifications and Supplements. cates: which, however, did not Change the System of the property classes in principle. This draf? was then minirnum tcnsile strengt.h and yield to ultimate revised once more. A second draft was prepared in stress ratio. 1977 and has since been adopted by a Iarge majority of the member bodies of ISO. While considerable EXAMPLE effort was required to develop thoroughly this draft concerning property classes for bolts and screws, it Property class 8.8 was finally resolved to %Z; s;aZisiaction of the interested countries within Sub-Committee SC 1 of First figure (“8” in 8.8) = l/lOO of the iSO/TC 2 and now is aqreed to by ISO. More exten- mininium tensile strength, in newtons per sive by far, and touching the substance of the Square millimetre. specifications, was the work on a revised Version of the ISO Recommendation ISO/R 898-2 and its con- Second figure (If8” in 8.8) = ‘IO times the version into an ISO Standard on property classes for yield stress ratio (0,8). nuts.

Multiplication of these two figures Experience had shown that, while the concept of (8 x 8 = 64), == l/lO of the minimurn yield property classes in conjunction with a norninaI 0,81.) stress, in newtons per Square millimetre. nut height is simple and straightforward, certain practical difficuities arise. First, it is sometimes dif- b) In the case of nuts: ficult or impossible to achieve specified nut properlies with the most econornical materials and designation number = l/lOO of the minimum methods, for example with fine threads and certain tensile strength, in newtons per Square miiii- sizes of coarse threads. Secondly, compliance with melre, of a bolt and screw, which, when rnated the requirernents does not necessarily provide the with the nut, tan be loaded up to the minimum assurance that the assembly would resist thread yield stress. stripping during tightening. Previously it was con- sidered adequate if the nut proof load was designed EXAMPLE equal to the holt minimum ultirnate strength, however, the advent of yield Point tightening methods Roll or screw 8.8 - nut 8 and improved understanding of the interaction between nut and bolt threads showed the nuts required connection loadablc up to minimum yield re-design to provide greater resistance to stripping stress of the holt or screw. of both the internai and extemal threads.

12 ISO 8984:1992(E)

For exampie, consider that Ihe effective tensile discussed within Sub-Committee SC I as wetl as in strength of a holt of class 8.8 rnay be belween the various national committees. 800 N/mm2 and about 965 N/mrn’ (determined froni the maximum hardness) in sizes up to M16. Conse- Despite the initial retuctance of the committee to quently the yicld stress may range between permit changes in existing specifications, the test 640 N / m m * and 772 N/mnI* for a vield to ultimate prograrnme clearly indicated that there was inad- stress ratio of 80 9/0. With the uie of yield point equate resistance to assembly stripping, brought tighteninq it will be Seen that the tightening stress about Iargely by the improved tightening methods approaches Zhe proof stress. Recent research has, and upgrading of mechanicat properties. The prob- in addition, shown tlIat a nut tested with a hardened lem was both one of boit thread stripping and nut mandreI is capable of susfaining a higher ioad be- thread stripping, and, as a result, it was conciuded fore strippitIg than when tested with a boit of the ttIat the mosf viable means of overcoming the prob- appropriate property ctass. For exampie, a property lern was by increasing .the nominal 0,811 nut height class 8 nut when tesled with a mandrel of 45 HRC where required. It is not the purpose of this annex will be capable of approxirnately IO o/o higher load .to provide a detailed description of the tests con- than when lested with a properiy ctass 8.8 bolt of ducted and the nut design method devetoped, for dimensions simitar 10 the mandrel. Therefore. a nut which the reader is referred to the foilowing pubii- that just meets a proof stress of 800 N/mn? with a cation which provides a summary of resuits and the hardened mandret might only be expected t.o sustain nIcltIod employed: “Armlysis and Design of Threaded a load of approxirnately 720 N/mm* when mated with Assemblies”, E.M. Atexander, 1977 SAE Trans- a property class 8.8 holt of minimum dimensions. lt actions, Paper No. 770420. will be Seen that stt- ippi ng of fl1e t h read S may occu t The caicuiation for nuts of proper-ty ciasses 4 to 6 when t ightening fr0 st ress es in excess 0 f ttIis, and according to ttIe Alexander theory was not based on frorn the boit rnechanicai pro pert ies it will be seen tiIe maximum bolt hardness 250 HV, as given in that this could he a frequent acc u t-ren ce with yieid ISO 898-1, see tabie A.l, because this is a tlardness point tightening. lt might be aryued, however, thal: which may occur at the boit end or ttIe head oniy. under torque tension toading the tensile strengtlI of Therefore it was agreed to make caicuiations on the the holt is reduced by about 15 %G, bu1 it shoutd also basis of the effective maximunI hardnesses within be realized that the stripping strenylh of the as- . I the thread engagement part of the holt, which are sembly is also reduced by almost the Same amount qiven in table A.2. under tot-q ue te nsion loading. In addition to t.he in- \ froduc tian of yield Point tighfening mettIods, Simiiar graduated hardness vaiues were specified changes in certain ISO Standards were under con- in ISO/R 898-1:1968. sideration that would also adversely affect ttiis stripping tendency. Upgrading of bolt and screw The above work showed that many factors influ- mechanical properlies was pt-oposed as shown in enced resistance of the stripping of threads, inciud- iabie A.? (which is an excerpt from ISO 898-l), the ing folerances, pitch, beit mouthing of nut minor pur-pose of which was to utilize futly the availabte dianIeter, size of countersink in nut, relative strengfh strength of the commonly used materiats for grades of nut threads to bolt threads, tength of engagemenf, 4.8, 5.8, 8.8 (above M16), 10.9 and 12.9. width across fiats of nut, and styie (for exampte hexagon flange), coefficient of friction, number of ttIreads in the grip, etc. Analysis of the various sizes Another proposed Change u nder consideration at of fasteners on this basis indicated .that it was not this tin ‘Ie wa s 1.0 reduce ttIe wid ttI across fl ats of appropriate to have a fixed nominal nut height, for certain stzes of h exagon prod ucts to provide econ- exampte 0,811 as before, but rather each Standard omies through optimized materiat use. As a resutt assembiy shouid be designed to give a suitable re- of these and other factors, certain mernber countries sistance to stripping. The resuit of this anaiysis (Canada, Germany, NettIertands, Sweden, UK, USA) gives the nut heights shown in table A-3. of Sub-Cornmittee SC 1 of tSO/TC 2 conducted research and extensive testing of nut-bott assen-ibties. It will be Seen that .there are two stytes of nut, Tests inciuded a fuit va riety of prod uct sizes, styie 2 being approximateiy 10 % highet- than streng fl7 ieveis and nIate riais. in xqeneral, test s were styie 1. Styie 1 height is intended for property conducted on typical production fasteners utiiizing ciasses 4, 5, 6, 8, 10 and 12 (up to M16) in conjunc- Standard matet-ials. Test Parts were accurately tion with appropriate mechanical propel-ties, while measured for dimensions and material stt-ength style 2 dimensions are intended for use with prop- which then aiiowed appropriate statisticai inferpret- erty ciasses 8, 9 and 12, also with appropriate me- ation of the data. Results of the various invesfigaiors chanicat properties. The higher style of nut was were evaluated by Canada a n d fo u n d to corre t ate primarily developed as an economical cold-formed Welt. A yeneral\ series of for m jtae res\ rttcd t.hat nut to be used with property class 9.8 boits and could be apptied to predict the assembly strength screws and it also provides suitabte dimensions for of threaded components with ihe ISO 68 basic a heat-treatabte nut of good ductility for use with thread p rofi t e. These fi nd i n qL s were property class 12.9 botts and screws. The intended

13 ISO 898-2:1992(E)

applications of the two styles of nuts at-e detaiied in The values of table 5 are only related to nuts with table 5, ft-om which it is seen that this additional style coarse thread. The Same applies also to the test of nut does not mean that dual stocking of pst-t ge- loads given in table 1. For t-Us with fine pitch tht-ead, ometry will result. see ISO 898-6.

An overlapping between style 1 and style 2 occurs The loads given in table 1 at-e based on a test only in two cases. In the case of style 1, property mandrel as specified in this part of ISO 898 with a class 8 allows the employment of nuts, not minimum hardness of 45 HRC and thread tolerante quenched and tempered (cold-worked low-carbon of 5h6g (major diameter of 6g in the last quarter). steel) only up to and including M?6; above M16 the nut style 1 has to be quenched and tempered. How- ISO 898-1 and this part of ISO 898 on mechanical ever, it is possible in this case to use alternatively properties, ISO 4014 to ISO 4018 on hexagon bolts the thicker. not quenched and tempered, style 2. and screws, and ISO 4032 to ISO 4036 on hexagonal This is a question of economics in the final analysis. nuts have been published reflecting the revised In the case of property class 12, it is not appropriate mechanical properties, changes in nut heights and to use style 1 nuts above size M16. Due to the re- changes in width across flats (width across flats of quired proof foads, it would be necessary to raise MIO, M12, M14 and M22 revised to 16 mm, 18 r-nm, the hardness of the nut to such an extent that its 21 t-nm and 34 mm respectively fror-n 17 mm, ductility, which is necessary from the functional 19 mm, 22 mm and 32 mm) as recommended by Point of view, would be impaired. Hence, the thicker ISO/TC 2. style 2 nuts quenched and tempered are necessary This part of ISO 898 makes the following Statement in this case. If necessary, it would be possible to concerning the property classes for nuts with full restritt the use of these nuts to sizes above M16, so loadability: that then no overlapping between style 1 and style 2 would occur in the case of property class 12. A bolt or screw of a particuiat- propet-ty class as- Once nut dimensions were determined based on sernbled with the equivalent pt-operty class of assembly strength criteria, the proof loads of these nut, in accordance with table 2, is intended to nuts with a restricted size hardened rnandrel were provide an assembly capable of being tiqhtened determined. The t-esult was that Stresses under to achieve a bolt tension equivalent to ihe bolt proof load were not constant for each property class proof Load or yield load without stripping. Ad- of nut brit varied with size. Accordingly, table 5 ditionally, geometry and mechanical proper-ties Shows revised Stresses under proof load and hard- of nuts up to M39 and property class 12 of 6H ness values for nuts. The property classes 04 and thread tolerantes are designed to pt-ovide fot- a 05 (previousiy 06) for hexagon lhin nuts with result- high deqree of t-c-tskpl,~ nee lo sirlpping (at least ant reduced loadability are also indicated in this ta- IO % b&t breakage of individual lots even under ble. These nuts incidentally were not designed to adverse minimum material conditions) when in- provide resistance to stripping and are simply based advertently overtorqued, in ot-der to warn the on a fixed height of 0,61). user- that the installation practice is not appropriate. Phe stresses under proof load given in table 5 are fot the Standard tolerante of 6H usually applied to nuts Certain users of the referenced Standards could not! for mechanical fasteners. Where a Iarger tolerante of necessity, participate in their detailed develop- or allowance is applied, these Stresses should be ment and it is hoped that this explanatory note will modified by a factor as shown in table 1. provide increased understanding of this reIatively complicated subject.

Table A.1 - Property classes for bolts and screws

3.6 4.6 4.8 5.6 5.8 6.8 8.8 0.8 10.9 12.9 Property class < M16 > M16

Tensile num. 300 400 490400 590 500 600 800 800 900 1 000 1 200 strength, A, ------.-- .--.-. _--___-_------,-.----w-e -.--- -__. ------.---_-~-_.------~-- .---__--__~ -_____I_____ ~ --.-__.____ ---. ---_-- -___-~~ __-__-_------_-___ .--_--.< _ Pl /m r-r-+ min. 330 400 420 500 520 600 800 830 900 1 040 1 220 _------_-__----.---___-----_------, ------_-_--, -----~--_-__~_ .---__._-__.-__ __._~__ -____.____._-_ ___.____._-_ -- -.--.------.--.------, ._-----.-----..------_--_------+- --__ -~-- -..-..- --_---_-I_------_---____ - -. Vickers hard- max. , 250 t IV I 250 t iV l 250 t-wt-iV l 259 I-iV 250 tivHV 250 t-iV l 320 tivtiV l 335 t-wt-W I 360 tivt iV I 380 t-W 435 t-iVHV ness 259tIV 250 tiv L II ------.

34 ISO 898-2:1992(E)

Table A.2 - Effective maximum hardness within the thread engagement part of the bolt Praperty class Maximum hardness 1 3.6 158 HV 4.6; 4.8 180 I-IV 5.6; 5.8 220 HV 6.8 250 HV

Table A.3 - Heights of hexagon nuts

Nut height

______-_ w---_--_I_e_------P--P ----- Width across flats Styie 1 styk? 2 Thread ___-..-- __~_ ------min. max. min. max. rn/ Zl mm mm mm mm mm

MS 8 44 477 0,94 498 51 1,02 _-~_- __------~-~ ----- M6 10 4.9 572 0,87 594 5,7 0,95 ___._-_----~._-_-_~-_ -. ---- _----~~.- -___- ~_-~-I_-----_- - a,.-- M7 11 6,14 6,50 0,93 6,84 7,20 1,03 ___~ ---_--PP------_--~-__. M8 13 6,44 6,80 0,85 7,14 7,50 0,94 _~_I-.-_--.-.------.I -~-__------_I__ .~------~--- MIO 16 8,04 8,40 0,84 8,94 9,30 0,93 _.I __-.__-_--_--_~_. ___~__ __-_ -._---_-.-. ---- ._--"------__._-__ __-._ J------_ ,_I-_------I_----.---- .----.---- M12 18 10,37 IO,80 0,90 11,57 12,00 l,oo _~ __.______-_- -...- --.- ---- __p--e..--- -.------I Ml4 21 12,l 12,8 0,91 13,4 14,l 1,Ol _-___^____ ------.- ---. _-~------Ip--._------_ ------.. Ml6 24 14,l l4,8 0,92 15,7 16,4 1,02 _-____.___--_ .-- ._--_----- .-- ___-___I----I_~---_ _.____----. _-_--__- --..-----.---P-u M18 27 15,l 15,8 0,88 16,9 17,6 0,98 _-.___~------_ - -~ --- --_--_-.---__------__--..-..-w-----v ._-. M20 30 16,9 18,0 0,90 19,0 20,3 1,02 _-,-______-- P-----P------M22 34 18,l 19,4 0,8R 20,5 21,8 0,93 ..__~- --.----~----I-- ___--- __~---_--_--_L-----.-.-~- M24 36 20,2 21,5 0,90 22,6 23,9 l,oo _____ -y._------"l--p------M27 41 22,5 23,8 0,88 25,4 26,7 0,99 _- ___-_-__---.---~.--- .--_l_------~ -- - - ,,_-----..------P M30 46 24,3 25,6 0,85 27,3 28,6 0,95 ___- -.------_-- ____- -~------~- ---., ~- m---.---p M33 50 27,4 28,7 0,87 30,9 32,5 0,98 l_-l~------_-r_ ._-. ------_-_~-- -_.------1 -- _~_____~ M36 55 29,4 31,0 0,136 33,l 34,7 0,96 ______-___.-.-_- --._.-.-. -- _-___ __-__--_-__------_-.-__- - _----_._----_----. ___ __ .___-_ ------.--.-PI ------.- - _----~-- M39 60 31,8 33,4 0,86 35,9 37,5 0,9G PP

15 ISO 898-2:1992(E)

Annex B (informative)

Bibliography

[l--j ISO 3506:1979, Corrosion-resistan t s tainless [S] ISO 4018:1988, Hexagon head screws - Prod- steel fasteners -- Specifications. uc t grade C.

[2] ISO 4014:1988, Hexagon head bolts -- Product ISO 40323986, Hexagon nuts, sfyle I -- Product grades A and B. grades A and 8.

ISO 4015:1979, Hexagon head bolts ~ Product [8] ISO 4033:1979, Hexagon nuk, style 2 -- Producf grade 8 -- Reduced hanh (slw?k diameler ap- grades A and B. proximately egual to pitch diameter-). [9] ISO 40341986, Hexagorj nuts - Product grade ISO 4016:1988, Hexaqon.. head bolts - Product C. grade C. - [ IÖJ ISO 4035:1986, Hexagon thin nuts (chamfered) [5] ISO 4017:1988, Hexagon head screws - Prod- -- Product gradesL A and B. uct grades A and B. ’ [ 1 l] ISO 4036:1979, Hexagon thin nuts - Product grade B (urhamfered}.

16 This page intentionally left blank ISO 898-2:1992(E)

-- p-w------~ ----PP- -- _.-- - .-__l-_<-_----- . . .--.---- _-- -- . ----.--- .--.I__------I-M------*-.------.- .------_.------______l_-_l_l. ~ ---._--_--.------.~- - -.------_-.-- _------UDC 621.882.3

Descriptm: Fastwem, twtc; (fastenws), coarse threads, specifications, mechanical properties, tests, designation, rrvuking.

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