Flat washers are used to increase the bearing surface of a bolt head or nut and distribute pressure away from the points of the hex or square. For every bolt or screw diameter, there are infinite possibilities for the inner diameter, outer diameter and thickness of the accompanying flat washer. In order to make the selection of a flat washer easier, certain standards have evolved.
The majority of flat washers in inventory at Nickel Systems conform to what we call a Commercial Standard. They are not dimensionally equivalent to USS (United States Standard) pattern, however, some sizes do match the SAE (Society of Automotive Engineers) pattern. The inner diameter is large enough to accommodate a bolt shank at the high side of tolerance. In the interests of economy when flat washers are made from stainless or nickel-based alloys, outer diameters and thicknesses are only as large as functionally needed.
Nickel Systems maintains an inventory of commercial flat washers in Hastelloy® (Alloys C276, C22, B2), Carpenter® 20 (Alloy 20), Duplex 2205, 18-8 and 316 Stainless. Current inventory also includes Inconel® (600, 625), 310 Stainless, 316L Stainless, 317L Stainless and Monel® (Alloy 400).