Fastener Basics (PDF)

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Fastener Basics

Common Fastener Types Fastener Materials Hex bolts, or hex cap screws, are used in Note: Do not rely on this guide for color-matching. The machinery and construction. Can be used with a appearance of these materials sometimes differs signifi- nut, or in a tapped hole. Fully threaded hex bolts cantly from the photos below. are also known as tap bolts. Zinc-plated steel is a low carbon steel for Wood screws have large threads and a smooth general use. Relatively shank f or pulling two pieces of material together. inexpensive, with the They can be used in wood and other soft materi- zinc plating providing als. moderate corrosion Sheet metal screws have sharp points and resistance suitable for threads, and are designed to be driven directly indoors or otherwise into sheet metal. They can also be used in softer dry conditions. Color is materials like plastic, fiberglass, or wood. either a blue-ish tint or Machine screws are fully threaded for use with a yellow depending on the exact process. nut or in a tapped hole. Certain types are some- Hot-dipped galvanized times referred to as stove bolts. steel has a thicker zinc Socket screws are machine screws with an coating for better internal hex socket (Allen) drive. Longer lengths corrosion resistance, may have a smooth shank. making it suitable for outdoor use. Because Lag bolts, or lag screws, are large wood screws of the thick plating, with hex heads. Typically used for wood only galvanized nuts and washers will fit construction and landscaping. galvanized bolts. The coating typically has a Carriage bolts have smooth, domed heads with rough, dull grey finish. a square section underneath that pulls into the Stainless steel offers material to prevent spinning during installation. good corrosion Nuts are used to fasten machine threaded resistance, making it fasteners in through-hole applications. Lock nuts suitable for outdoor help prevent loosening. use and marine applications, but is Washers spread the load over a greater surface more expensive than zinc plated. area when tightening a bolt, screw or nut. Lock washers help preventing loosening. Chrome and nickel plated steel are smooth and polished Tip: Find a more comprehensive fastener type chart at http://boltdepot.com/info for appearance. The plating offers moderate corrosion resistance. Grade/Class & Fastener Strength Brass and bronze are Fastener Grade (US) or Class (metric) refers to the mechanical proper- copper alloys with good ties of the fastener material. Generally, a higher number indicates a corrosion resistance. stronger, more hardened (but also more brittle) fastener. More expensive than For a chart of fastener grades, head markings and mechanical properties, see steel, these materials Bolt Depot’s Grade markings and Strength Chart at http://boltdepot.com/info are typically used for decorative applications. US bolt head markings Metric bolt head markings Colors can vary significantly. Alloy steel is highly 8.8 10.9 12.9 hardened and usually Low Carbon Grade 5 Grade 8 Class 8.8 Class 10.9 Class 12.9 black oxide and/or oil coated, offering little Note: In addition to these markings, the head will often have a manufacturer stamp. corrosion resistance.

Machine screws, Phillips pan head, Stainless steel 18-8, #12-24 x 1"

Fastener type Material Diameter Length Thread Count (TPI) Drive Types Head Styles Measuring Diameter Phillips and Slotted Hex heads are typically For most drives are common used with larger bolts and types of Diameter Phillips Slotted in screws, but prone screws, and tightened with a fasteners, to cam-out wrench. the diameter (stripping). Pan heads have a slightly is measured on domed head that sits above the outside of Diameter Combo drives, that the surface. the threads. can be used with Combo either driver, are Flat heads are installed in a Note: US diameters under 1/4” are given as numbers (e.g. available for many countersunk hole for a flat #12) instead of inches, in order of increasing size. If you need fastener types. surface. to find the actual diameter, use a table corresponding to your fastener type at http://boltdepot.com/info Frearson and Pozidriv Round heads are tall domed are similar to Phillips, heads, used primarily for Frearson Pozidriv but less prone to decorative purposes. cam-out. Thread Count & Thread Pitch Oval heads are a low domed and countersunk Machine threaded fasteners specify a thread Hex socket (Allen) density in Threads Per Inch (US) or as a Thread drives are compact heads, used primarily for decorative purposes. Pitch in mm (Metric). Hex socket and easy to drive, but (Allen) prone to cam-out. Truss heads are slightly For a given diameter, a fastener may be available domed, with a wide head for in coarse (standard), fine and sometimes super Star and Square drive an extra large surface area. fine thread. are resistant to cam-out and can be Socket heads are narrow Star Square with a socket drive, and (Robertson) installed single- handed. knurled or smooth sides. Measuring Length Button heads feature a Fastener length is Note: Most drive types (Frearson and Slotted medium dome. Typically usually measured from being notable exceptions) require the correct used with a hex socket where the material is driver size for proper installation. drive. assumed to be to the end of the fastener. Length Thus, countersunk Nut & Washer Sizes fasteners are measured overall and non-counter- Nut and washer sizes indicate the screw or bolt they fit. For example: sunk fasteners are measured from under the Length head.

3/8”-16 Hex Bolt 3/8” Washer 3/8” -16 Nut More Information Different washer patterns have different outside diameters. For example, hardened US washers are At http://boltdepot.com/info you'll find: available in USS (wider) and SAE (narrower) • In-depth fastener info patterns. Fender washers have large outside diameters. • Charts and tables • Printable lay-over charts and tools for quickly identifying fastener sizes 1/4” 1/4” 1/4” x 1” and types SAE USS Fender • Much more...