Convert flat washer sizes between SAE, USS, and metric dimensions. Pick a bolt size or enter a measured washer inside diameter to compare ID, OD, thickness, inches, millimeters, and nearby alternatives.
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This chart lists common approximate flat washer dimensions. Use it for quick comparison, then check the exact standard, finish, grade, and supplier drawing for critical assemblies.
| Washer | Inside diameter | Outside diameter | Thickness | Notes |
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For the same nominal bolt size, USS washers usually have a larger outside diameter than SAE washers. Metric flat washers are sized around metric bolts such as M6, M8, and M10. The closest diameter may fit, but the bearing surface and thickness can still be different.
A common 1/4 inch SAE flat washer has an approximate 0.281 inch inside diameter, 0.625 inch outside diameter, and 0.051 inch thickness. That is about 7.14 mm ID, 15.88 mm OD, and 1.30 mm thick.
No. They are close, but not identical. A common M6 flat washer has about a 6.4 mm ID, while a 1/4 inch SAE washer is about 7.14 mm ID and a 1/4 inch USS washer is about 7.92 mm ID.
USS washers are generally larger in outside diameter than SAE washers for the same nominal bolt size. That extra width spreads load over more surface area.