PRODUCT SPECIFICATIONSPart #: 0000-130951Fastener Type: Flat Washer USS PatternSize Description: 5/16"Diameter/Nominal Size: 5/16"*Inside Diameter: 0.375"Outside Diameter: 0.875"Thickness: 0.064-0.104"System of Measurement: InchGrade: 2Material: Low Carbon SteelFinish: Zinc PlatedUsed with: Bolts/Screws up to Grade 5Average Piece Weight: 0.0120500 lbs.*Washer Sizing: Washer sizes are nominal (sized for the bolt that the washer will fit). Actual inside diameter is almost always larger than stated size. Please see the Inside Diameter spec in the table above, if available.Washers are thin disk-shaped plates with a hole that is used to distribute the load of a threaded fastener such as a bolt or nut; often have an outer diameter (OD) about twice their inner diameter (ID), but this can vary based upon the washer. Washers come in many different varieties; flat washers, split lock washers, toothed lock washers, beveled washers in both steel and iron, etc.