WASHERS

In general, washers are used to increase the bearing surface of a nut or fastener's head, provide a smooth mating surface or protect the surface from damage when the nut or head is rotated, compensate for oversized or irregular shaped holes, space or shim parts, or to resist loosening. Common washers are listed below, or click on a type above for detailed information.

Washer size refers to its nominal hole size and is based on screw size. Its outside diameter (OD) is always larger. Size and OD are usually specified in fractional inches, although decimal inches may be used instead. Thickness is typically listed in decimal inches although we often convert it to fractional inches for convenience.

Hardened and high strength alloy washers are used with graded fasteners, such as ASTM A325 and SAE Grades 5 and 8—see specific washers for details.

Depending on the washer type, common materials include aluminum, brass, nylon, silicon bronze, stainless steel and steel. Finishes include nickel for brass and steel, and hot dip galvanizing and zinc plating for steel. Unplated and uncoated steel washers—referred to as plain finish—may also be available and are susceptible to rust. Not all washer types are available in all materials and finishes.

**Table 1. Washers.** A listing of common washer types and styles.
WASHERS
Backup Washers
Rivet Backup Washers
Beveled Washers
Hardened Beveled Washers Malleable Beveled Washers
Finishing Washers
Countersunk Finishing Washers
Flat Washers
Fender Washers Machine Screw Flat Washers Mega Thick Flat Washers SAE Flat Washers Square Plate Washers Structural Flat Washers Thick Flat Washers T-Slot Washers USS Flat Washers	Fender Flat Thick Square Plate T-Slot
Lock Washers
Hi-Collar Lock Washers Lock Set Pair Lock Washers Split Lock Washers Tooth Lock Washers	Hi-Collar Lock Set Pair Split Tooth
Sealing Washers
Metal Backed Neoprene Sealing Washers

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