SAE vs USS Flat Washers

ASME B18.21.1 · USS and SAE flat washers

What it is

FIELD IDENTIFICATION

USS and SAE are two inch flat-washer series. USS is wider and usually thicker; SAE fits closer to the

bolt with a smaller outside diameter.

USS (larger OD)

SAE (smaller OD)

Same bolt size, different outside diameter

Nominal dimensions, in (ID x OD x thickness)

Bolt

USS

SAE

1/4

5/16 x 3/4 x 0.065

9/32 x 5/8 x 0.065

5/16

3/8 x 7/8 x 0.083

11/32 x 11/16 x 0.065

3/8

7/16 x 1 x 0.083

13/32 x 13/16 x 0.065

7/16

1/2 x 1-1/4 x 0.083

15/32 x 59/64 x 0.065

1/2

9/16 x 1-3/8 x 0.109

17/32 x 1-1/16 x 0.095

5/8

11/16 x 1-3/4 x 0.134

21/32 x 1-5/16 x 0.095

3/4

13/16 x 2 x 0.148

13/16 x 1-15/32 x 0.134

7/8

15/16 x 2-1/4 x 0.165

29/32 x 1-3/4 x 0.134

1

1-1/16 x 2-1/2 x 0.165

1-1/16 x 2 x 0.134

Nominal values; check the current ASME B18.21.1 / ASTM F844 tables for tolerances.

Key points

Flat washers are identified by dimensions, not a stamp. Neither is hardened; use F436 under structural bolts.

Governing standards: ASME B18.21.1-2009 (R2016); ASTM F844. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always

take precedence over this sheet.

torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability

arising from reliance on this reference.