U.S. Bolts - Head and Wrench Sizes

Reference guide for hex bolt, lag bolt, square bolt, and heavy hex bolt head and wrench sizes. Includes diameter to wrench size conversions with conversion factor of 1 in = 25.4 mm. Based on ANSI/ASME B18.2.1 standards.

Bolt Diameter (in)Hex Bolt / Lag Bolt / Square Bolt (in)Heavy Hex Bolt (in)
#61/4
#81/4
#105/16
#125/16
1/47/16 or 3/8
5/161/2
3/89/16
7/165/8
1/23/47/8
9/1613/16
5/815/161 1/16
3/41 1/81 1/4
7/81 5/161 7/16
11 1/21 5/8
1 1/81 11/161 3/4
1 1/41 7/82
1 3/82 1/16
1 1/22 1/4
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Bolt Diameter-- mm

Reference Information

  • 1 inch = 25.4 mm
  • Standard: ANSI/ASME B18.2.1 Square, Hex, Heavy Hex, and Askew Head Bolts and Hex, Heavy Hex, Hex Flange, Lobed Head, and Lag Screws (Inch Series)
  • Bolt Types: Hex Bolt, Lag Bolt, Square Bolt, Heavy Hex Bolt
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