Before hex bolts gained prominence, square head machine bolts happened to be the industry standard. Today, square bolts are commonly used to serve aesthetic purposes, providing a rustic finish in a new structure as well as to match any existing fasteners of an older structure. Sometimes, square lag screws are used to serve these purposes as well. Cross arm bolts or machine bolts are generally supplied to the utility industry wherein an added cone point is included.

Manufacturing

Baseline Bolt manufactures premium quality square bolts of diameter 1/2″ - 2″ fulfilling most of the ASTM, AASHTO, & SAE specifications. Moreover, it is possible to create special tooling in order to produce nonstandard bold heads or head dimensions with the name and/or logo of your company. Baseline Bolt also stocks square head blanks to be used for expedited deliveries or small orders.

Stock

baseline Bolt does not stock any square head machine bolts, and in most cases, square head bolts are not readily available through fastener distributors. Typically, square head bolts will need to be custom manufactured.

Standard Thread Lengths

Bolt lengths < 6″: Thread length = (2 X diameter) + 1/4″
Bolt lengths > 6″: Thread length = (2 X diameter) + 1/2″

Square Head Dimensions

Click table to show drawing
Bolt Diameter D F C H
Body Diameter Width Across Flats Width Across Corners Height
Max Basic Max Min Max Min Basic Max Min
1⁄2 0.515 3⁄4 0.750 0.725 1.061 0.995 21⁄64 0.348 0.308
5⁄8 0.642 15⁄16 0.938 0.906 1.326 1.244 27⁄64 0.444 0.400
3⁄4 0.768 11⁄8 1.125 1.088 1.591 1.494 1⁄2 0.524 0.476
7⁄8 0.895 15⁄16 1.312 1.269 1.856 1.742 19⁄32 0.620 0.568
1 1.022 11⁄2 1.500 1.450 2.121 1.991 21⁄32 0.684 0.628
11⁄8 1.149 111⁄16 1.688 1.631 2.386 2.239 3⁄4 0.780 0.720
11⁄4 1.277 17⁄8 1.875 1.812 2.652 2.489 27⁄32 0.876 0.812
13⁄8 1.404 21⁄16 2.062 1.994 2.917 2.738 29⁄32 0.940 0.872
11⁄2 1.531 21⁄4 2.250 2.175 3.182 2.986 1 1.036 0.964
13⁄4* 29⁄16 13⁄16
2* 215⁄16 15⁄16

* ASME only defines head dimensions up to 1-1/2". Dimensions for 1-3/4 and 2" are approximate and not covered under the ASME dimensional specifications.

Dimensions per ASME B18.2.1 1996