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.

Crossarm 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″

Square Head Dimensions

Click table to show drawing
Bolt DiameterDFCH
Body DiameterWidth Across FlatsWidth Across CornersHeight
MaxBasicMaxMinMaxMinBasicMaxMin
1⁄20.5153⁄40.7500.7251.0610.99521⁄640.3480.308
5⁄80.64215⁄160.9380.9061.3261.24427⁄640.4440.400
3⁄40.76811⁄81.1251.0881.5911.4941⁄20.5240.476
7⁄80.89515⁄161.3121.2691.8561.74219⁄320.6200.568
11.02211⁄21.5001.4502.1211.99121⁄320.6840.628
11⁄81.149111⁄161.6881.6312.3862.2393⁄40.7800.720
11⁄41.27717⁄81.8751.8122.6522.48927⁄320.8760.812
13⁄81.40421⁄162.0621.9942.9172.73829⁄320.9400.872
11⁄21.53121⁄42.2502.1753.1822.98611.0360.964
13⁄4*29⁄1613⁄16
2*215⁄1615⁄16

* 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