What dimensional standards do stainless steel flat washers meet?

Stainless flat washers fall under the same ASME dimensional standards as your typical plain steel flat washer, which is ASME B18.21.1. Under ASME B18.21.1, dimensional tolerances for plain washers, there are two types specified, type A and type B. Type A has two series sizes to consider which include narrow and wide, while Type B has three series sizes including narrow, regular and wide. As you can probably guess, narrow is going to have the smaller thickness and outside diameter in comparison to wide, with series regular falling in-between. Although the difference between the three is minimal, depending on the source of the stainless washers, any of these series could be supplied. Therefore, if the application is critical with regard to washer dimensions, you may need to specify which type and series is required or preferred.

The above mentioned dimensions can be found in the Industrial Fasteners Institute (IFI), Inch Fasteners Standards Book, within the Washers section.

Dimensions of Type A Plain Washers
Normal Washer Size Series (1) A B C
Inside Diameter Outside Diameter Thickness
Basic Tolerance Basic Tolerance
Plus Minus Plus Minus Basic Plus Minus
1/4 (0.250) N 0.281 0.015 0.005 0.625 0.015 0.007 0.065 0.080 0.051
1/4 (0.250) W 0.312 0.015 0.005 0.734 (2) 0.015 0.007 0.065 0.080 0.051
3/8 (0.375) N 0.406 0.015 0.005 0.812 0.015 0.007 0.065 0.080 0.051
3/8 (0.375) W 0.438 0.015 0.005 1.000 0.030 0.007 0.083 0.104 0.064
1/2 (0.500) N 0.531 0.015 0.005 1.062 0.030 0.007 0.095 0.121 0.074
1/2 (0.500) W 0.562 0.015 0.005 1.375 0.030 0.007 0.109 0.132 0.086
5/8 (0.625) N 0.656 0.030 0.007 1.312 0.030 0.007 0.095 0.121 0.074
5/8 (0.625) W 0.688 0.030 0.007 1.750 0.030 0.007 0.134 0.160 0.108
3/4 (0.750) N 0.812 0.030 0.007 1.469 0.030 0.007 0.134 0.160 0.108
3/4 (0.750) W 0.812 0.030 0.007 2.000 0.030 0.007 0.148 0.177 0.122
7/8 (0.875) N 0.938 0.030 0.007 1.750 0.030 0.007 0.134 0.160 0.180
7/8 (0.875) W 0.938 0.030 0.007 2.250 0.030 0.007 0.165 0.192 0.136
1 (1.000) N 1.062 0.030 0.007 2.000 0.030 0.007 0.134 0.160 0.108
1 (1.000) W 1.062 0.030 0.007 2.500 0.030 0.007 0.165 0.192 0.136
1-1/8 (1.125) N 1.250 0.030 0.007 2.250 0.030 0.007 0.134 0.160 0.108
1-1/8 (1.125) W 1.250 0.030 0.007 2.750 0.030 0.007 0.165 0.192 0.136
1-1/4 (1.250) N 1.375 0.030 0.007 2.500 0.030 0.007 0.165 0.192 0.136
1-1/4 (1.250) W 1.375 0.030 0.007 3.000 0.030 0.007 0.165 0.192 0.136
1-3/8 (1.375) N 1.500 0.030 0.007 2.750 0.030 0.007 0.165 0.192 0.136
1-3/8 (1.375) W 1.500 0.045 0.010 3.250 0.045 0.010 0.180 0.213 0.153
1-1/2 (1.500) N 1.625 0.030 0.007 3.000 0.030 0.007 0.165 0.192 0.136
1-1/2 (1.500) W 1.625 0.045 0.010 3.500 0.045 0.010 0.180 0.213 0.153
1-5/8 (1.625) -- 1.750 0.045 0.010 3.750 0.045 0.010 0.180 0.213 0.153
1-3/4(1.750) -- 1.875 0.045 0.010 4.000 0.045 0.010 0.180 0.213 0.153
1-7/8 (1.875) -- 2.000 0.045 0.010 4.250 0.045 0.010 0.180 0.213 0.153
2 (2.000) -- 2.125 0.045 0.010 4.500 0.045 0.010 0.180 0.213 0.153
2-1/4 (2.250) -- 2.375 0.045 0.010 4.750 0.045 0.010 0.220 0.278 0.193
2-1/2 (2.500) -- 2.625 0.045 0.010 5.000 0.045 0.010 0.238 0.280 0.210
2-3/4 (2.750) -- 2.875 0.065 0.010 5.250 0.065 0.010 0.259 0.310 0.228
3 (3.000) -- 3.125 0.065 0.010 5.500 0.065 0.010 0.284 0.327 0.249
Dimensions of Type B Plain Washers
Normal Washer Size (1) Series A B C
Inside Diameter Outside Diameter Thickness
Basic Tolerance Basic Tolerance
Plus Minus Plus Minus Basic Plus Minus
1/4 (0.250) Narrow 0.281 0.015 0.005 0.500 0.015 0.005 0.063 0.071 0.056
Regular 0.281 0.015 0.005 0.734 (2) 0.015 0.007 0.063 0.071 0.056
Wide 0.281 0.015 0.005 1.000 0.015 0.007 0.063 0.071 0.056
3/8 (0.375) Narrow 0.406 0.015 0.005 0.734 (2) 0.015 0.007 0.063 0.071 0.056
Regular 0.406 0.015 0.005 1.000 0.015 0.007 0.063 0.071 0.056
Wide 0.406 0.015 0.005 1.250 0.030 0.007 0.100 0.112 0.090
1/2 (0.500) Narrow 0.531 0.015 0.005 1.000 0.015 0.007 0.063 0.071 0.056
Regular 0.531 0.015 0.005 1.250 0.030 0.007 0.100 0.112 0.090
Wide 0.531 0.015 0.005 1.750 0.030 0.007 0.100 0.112 0.090
5/8 (0.625) Narrow 0.656 0.030 0.007 1.250 0.030 0.007 0.100 0.112 0.090
Regular 0.656 0.030 0.007 1.750 0.030 0.007 0.100 0.112 0.090
Wide 0.656 0.030 0.007 2.250 0.030 0.007 0.160 0.174 0.146
3/4 (0.750) Narrow 0.812 0.030 0.007 1.375 0.030 0.007 0.100 0.112 0.090
Regular 0.812 0.030 0.007 2.000 0.030 0.007 0.100 0.112 0.090
Wide 0.812 0.030 0.007 2.500 0.030 0.007 0.160 0.174 0.146
7/8 (0.875) Narrow 0.938 0.030 0.007 1.469 (2) 0.030 0.007 0.100 0.112 0.090
Regular 0.938 0.030 0.007 2.250 0.030 0.007 0.160 0.174 0.146
Wide 0.938 0.030 0.007 2.750 0.030 0.007 0.160 0.174 0.146
1 (1.000) Narrow 1.062 0.030 0.007 1.750 0.030 0.007 0.100 0.122 0.090
Regular 1.062 0.030 0.007 2.500 0.030 0.007 0.160 0.174 0.146
Wide 1.062 0.030 0.007 3.000 0.030 0.007 0.160 0.174 0.146
1-1/8 (1.125) Narrow 1.188 0.030 0.007 2.000 0.030 0.007 0.100 0.112 0.090
Regular 1.188 0.030 0.007 2.750 0.030 0.007 0.160 0.174 0.146
Wide 1.188 0.030 0.007 3.250 0.030 0.007 0.160 0.174 0.146
1-1/4 (1.250) Narrow 1.312 0.030 0.007 2.250 0.303 0.007 0.160 0.174 0.146
Regular 1.312 0.030 0.007 3.000 0.030 0.007 0.160 0.174 0.146
Wide 1.312 0.045 0.010 3.500 0.045 0.010 0.250 0.266 0.234
1-3/8 (1.375) Narrow 1.438 0.030 0.007 2.500 0.030 0.007 0.160 0.174 0.146
Regular 1.438 0.030 0.007 3.250 0.030 0.007 0.160 0.174 0.146
Wide 1.438 0.045 0.010 3.750 0.045 0.010 0.250 0.266 0.234
1-1/2 (1.500) Narrow 1.562 0.303 0.007 2.750 0.030 0.007 0.160 0.174 0.146
Regular 1.562 0.045 0.010 3.500 0.045 0.010 0.250 0.266 0.234
Wide 1.562 0.045 0.010 4.000 0.045 0.010 0.250 0.266 0.234
1-5/8 (1.625) Narrow 1.750 0.303 0.007 3.000 0.030 0.007 0.160 0.174 0.146
Regular 1.750 0.045 0.010 3.750 0.045 0.010 0.250 0.266 0.234
Wide 1.750 0.045 0.010 4.250 0.045 0.010 0.250 0.266 0.234
1-3/4 (1.750) Narrow 1.875 0.300 0.007 3.250 0.303 0.007 0.160 0.174 0.146
Regular 1.875 0.045 0.010 4.000 0.045 0.010 0.250 0.266 0.234
Wide 1.875 0.045 0.010 4.500 0.045 0.010 0.250 0.266 0.234
1-7/8 (1.875) Narrow 2.000 0.045 0.010 3.500 0.045 0.010 0.250 0.266 0.234
Regular 2.000 0.045 0.010 4.250 0.045 0.010 0.250 0.266 0.234
Wide 2.000 0.045 0.010 4.750 0.045 0.010 0.250 0.266 0.234
2 (2.000) Narrow 2.125 0.045 0.010 3.750 0.045 0.010 0.250 0.266 0.234
Regular 2.125 0.045 0.010 4.500 0.045 0.010 0.250 0.266 0.234
Wide 2.125 0.045 0.010 5.000 0.045 0.010 0.250 0.266 0.234
2-1/4 (2.250) Narrow 2.375 0.045 0.010 4.000 0.045 0.010 0.250 0.266 0.234
Regular 2.375 0.045 0.010 5.000 0.045 0.010 0.250 0.266 0.234
Wide 2.375 0.065 0.010 5.500 0.065 0.010 0.375 0.393 0.357
2-1/2 (2.500) Narrow 2.625 0.045 0.010 4.500 0.045 0.010 0.250 0.266 0.234
Regular 2.625 0.065 0.010 5.500 0.065 0.010 0.375 0.393 0.357
Wide 2.620 0.065 0.010 6.000 0.065 0.010 0.375 0.393 0.357
2-3/4 (2.750) Narrow 2.875 0.045 0.010 5.000 0.045 0.010 0.250 0.266 0.234
Regular 2.875 0.065 0.010 6.000 0.065 0.010 0.375 0.393 0.357
Wide 2.875 0.065 0.010 6.500 0.065 0.010 0.375 0.393 0.357
3 (3.000) Narrow 3.125 0.065 0.010 5.500 0.065 0.010 0.375 0.393 0.357
Regular 3.125 0.065 0.010 6.500 0.065 0.010 0.375 0.393 0.357
Wide 3.125 0.065 0.010 7.000 0.065 0.010 0.375 0.393 0.357
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