Square head machine bolts were the industry standard prior to hex bolts gaining prominence. Square bolts are now most commonly used for aesthetic purposes to provide a rustic look in a new structure or to match existing fasteners in an older structure. Square lag screws are also used for these purposes.

Cross arm or machine bolts are commonly supplied for the utility industry and included an added cone point.

Manufacturing

Portland Bolt manufactures square bolts from 1/2″ diameter through 2″ diameter in most ASTM, AASHTO, and SAE specifications. Special tooling can be created to produce nonstandard head dimensions or bolt heads with your company’s name and/or logo. Portland Bolt stocks square head blanks that are used for small orders or expedited deliveries.

Stock

Portland 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″

Dimensions

Click table to show drawingSquare Head Bolt 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
3/8 0.388 9/16 0.562 0.544 0.795 0.747 1/4 0.268 0.232
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 1-1/8 1.125 1.088 1.591 1.494 1/2 0.524 0.476
7/8 0.895 1-5/16 1.312 1.269 1.856 1.742 19/32 0.620 0.568
1 1.022 1-1/2 1.500 1.450 2.121 1.991 21/32 0.684 0.628
1-1/8 1.149 1-11/16 1.688 1.631 2.386 2.239 3/4 0.780 0.720
1-1/4 1.277 1-7/8 1.875 1.812 2.652 2.489 27/32 0.876 0.812
1-3/8 1.404 2-1/16 2.062 1.994 2.917 2.738 29/32 0.940 0.872
1-1/2 1.531 2-1/4 2.250 2.175 3.182 2.986 1 1.036 0.964
1-3/4* 2-9/16 1-3/16
2* 2-15/16 1-5/16

* 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