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USS Flat Washer
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USS Flat Washer

USS Flat Washer

Low carbon USS flat washers are used under bolt heads or nuts to increase the bearing surface area, or to offer protection so that the nut or bolt can be rotated without distortion of the bearing surface. Flat washers are also used to give tightness to a joint, to prevent leakage, and especially to distribute pressure under the head of a bolt or nut. Dimensional specifications are governed by ASME B18.21.1. USS (United States Standard) flat washers have a larger outer diameter than SAE (Society of Automotive Engineers) flat washers, and can be utilized in nearly any application. ASTM F844 covers the standard specifications for unhardened steel flat washers for general use.

Governing StandardsUSS Flat Washer

ASTM F844 Covers standard, unhardened steel washers for general use.
ASME B18.21.1 Covers the dimensional requirements, physical properties, and related test methods for helical spring-lock washers (#0 through 3 inches), tooth-lock washers (#2 through 1 ¼ inches), and plain washers (#0 through 3 inches).

Dimensional SpecificationsUSS Flat Washer

USS Flat Washer dimensions
Per ASME B18.21.1-2009
Size Nominal A B C
Inside Diameter Outside Diameter Mean Section Thickness
Basic Tolerance
Plus		 Tolerance
Minus		 Basic Tolerance
Plus		 Tolerance
Minus		 Basic Max Min
#6 0.1380 0.1560 0.0080 0.0050 0.3750 0.0150 0.0050 0.0490 0.0650 0.0360
#8 0.1640 0.1880 0.0080 0.0050 0.4380 0.0150 0.0050 0.0490 0.0650 0.0360
#10 0.1900 0.2190 0.0080 0.0050 0.5000 0.0150 0.0050 0.0490 0.0650 0.0360
#12 0.2160 0.2500 0.0150 0.0050 0.5620 0.0150 0.0050 0.0650 0.0800 0.0510
1/4 0.2500 0.3120 0.0150 0.0050 0.7340 0.0150 0.0070 0.0650 0.0800 0.0510
5/16 0.3125 0.3750 0.0150 0.0050 0.8750 0.0300 0.0070 0.0830 0.1040 0.0640
3/8 0.3750 0.4380 0.0150 0.0050 1.0000 0.0300 0.0070 0.0830 0.1040 0.0640
7/16 0.4375 0.5000 0.0150 0.0050 1.2500 0.0300 0.0070 0.0830 0.1040 0.0640
1/2 0.5000 0.5620 0.0150 0.0050 1.3750 0.0300 0.0070 0.1090 0.1320 0.0860
9/16 0.5625 0.6250 0.0150 0.0050 1.4690 0.0300 0.0070 0.1090 0.1320 0.0860
5/8 0.6250 0.6880 0.0300 0.0070 1.7500 0.0300 0.0070 0.1340 0.1600 0.1080
3/4 0.7500 0.8120 0.0300 0.0070 2.0000 0.0300 0.0070 0.1480 0.1770 0.1220
7/8 0.8750 0.9380 0.0300 0.0070 2.2500 0.0300 0.0070 0.1650 0.1920 0.1360
1 1.0000 1.2500 0.0300 0.0070 2.5000 0.0300 0.0070 0.1650 0.1920 0.1360
1 1/8 1.1250 1.3750 0.0300 0.0070 2.7500 0.0300 0.0070 0.1650 0.1920 0.1360
1 1/4 1.2500 1.3750 0.0300 0.0070 3.0000 0.0300 0.0070 0.1650 0.1920 0.1360
1 3/8 1.3750 1.5000 0.0450 0.0100 3.2500 0.0450 0.1000 0.1800 0.2130 0.1530
1 1/2 1.5000 1.6250 0.0450 0.0100 3.5000 0.0450 0.0100 0.1800 0.2130 0.1530
1 5/8 1.6250 1.7500 0.0450 0.0100 3.7500 0.0450 0.0100 0.1800 0.2130 0.1530
1 3/4 1.7500 1.8750 0.0450 0.0100 4.0000 0.0450 0.0100 0.1800 0.2130 0.1530
1 7/8 1.8750 2.0000 0.0450 0.0100 4.2500 0.0450 0.0100 0.1800 0.2130 0.1530
2 2.0000 2.1250 0.0450 0.0100 4.5000 0.0450 0.0100 0.1800 0.2130 0.1530
2 1/4 2.2500 2.3750 0.0450 0.0100 4.7500 0.0450 0.0100 0.2200 0.2480 0.1930
2 1/2 2.5000 2.6250 0.0450 0.0100 5.0000 0.0450 0.0100 0.2380 0.2800 0.2100
2 3/4 2.7500 2.8750 0.0650 0.0100 5.2500 0.0650 0.0100 0.2590 0.3100 0.2280
3 3.0000 3.1250 0.0650 0.0100 5.5000 0.0650 0.0100 0.2840 0.3270 0.2490
  1. All dimensions are in inches.
USS Flat Washer
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Diameter Inside Diameter Outside Diameter Thickness Item # Availability Price Quantity UOM
1/4 0.3120 0.7340 0.0650 WFBL025 In Stock $0.01549/EA EA
5/16 0.3750 0.8750 0.0830 WFBL031 In Stock $0.04475/EA EA
3/8 0.4380 1.0 0.0830 WFBL037 In Stock $0.03989/EA EA
7/16 0.5 1.25 0.0830 WFBL043 3-5 Working Days $0.03906/EA EA
1/2 0.5620 1.3750 0.1090 WFBL050 In Stock $0.10826/EA EA
9/16 0.6250 1.4690 0.1090 WFBL056 In Stock $0.11025/EA EA
5/8 0.6880 1.75 0.1340 WFBL062 In Stock $0.21304/EA EA
3/4 0.8120 2.0 0.1480 WFBL075 In Stock $0.32076/EA EA
7/8 0.9380 2.25 0.1650 WFBL087 In Stock $0.37471/EA EA
1 1.25 2.5 0.1650 WFBL100 In Stock $0.46134/EA EA
1 1/8 1.3750 2.75 0.1650 WFBL112 In Stock $0.48962/EA EA
1 1/4 1.3750 3.0 0.1650 WFBL125 In Stock $0.58269/EA EA
1 3/8 1.5 3.25 0.18 WFBL137 In Stock $0.7275/EA EA
1 1/2 1.6250 3.5 0.18 WFBL150 In Stock $0.99468/EA EA
1 5/8 1.75 3.75 0.18 WFBL162 In Stock $1.50665/EA EA
1 5/8 2.0 4.25 0.18 WFBL187 In Stock $1.06791/EA EA
1 3/4 1.8750 4.0 0.18 WFBL175 In Stock $1.06096/EA EA
2 2.1250 4.5 0.18 WFBL200 In Stock $1.73803/EA EA
2 1/4 2.3750 4.75 0.22 WFBL225 In Stock $2.68037/EA EA
2 1/2 2.6250 5.0 0.2380 WFBL250 In Stock $4.45258/EA EA
3 3.1250 5.5 0.2840 WFBL300 In Stock $5.18699/EA EA