Square lag screws are used in wood construction and are often ordered for aesthetic purposes and provide a rustic look. Hex lag screws are more readily available in the marketplace as a standard stock item.


Manufacturing:

Fastindo Wiratama manufactures square lag screws from 1/2″ diameter through 1-1/2″ 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.
Unless otherwise specified, nonstandard lag screws manufactured by Fastindo Wiratama will possess a semi-cone point rather than a gimlet or cone point. A full point is unnecessary since a pilot hole nearly as large as the root diameter of the lag screw will need to be drilled prior to installation. Additionally, a gimlet point is designed for small diameter screws so they can be installed without a pilot hole. Lag screws in diameters listed in the above table do not require a gimlet point since too much torque would be required to install the large screws without drilling a pilot hole first. Without a pilot hole, the heads of the screws will often break before the lag is properly installed.

Standard Thread Length:

The minimum thread length for square lag screws shall be equal to half the nominal screw length plus 1/2″ or 6″, whichever is less. One should consider longer than standard thread lengths for lag screws which are extremely long.


Square Lag Dimensions
Bolt Diameter D F H Threads Per Inch Thread Dimension
Body Diameter Width Across Flats Head Height Pitch TF TD TR
Max Min Flat At Root Depth of Thread Root Diameter
1⁄2 0.515 0.482 3⁄4 11⁄32 6 0.167 0.072 0.064 0.371
5⁄8 0.642 0.605 15⁄16 27⁄64 5 0.200 0.086 0.077 0.471
3⁄4 0.768 0.729 11⁄8 1⁄2 41⁄2 0.222 0.096 0.085 0.579
7⁄8 0.895 0.852 15⁄16 37⁄64 4 0.250 0.108 0.096 0.683
1 1.022 0.976 11⁄2 43⁄64 31⁄2 0.286 0.123 0.110 0.780
11⁄8 1.149 1.098 111⁄16 3⁄4 31⁄4 0.308 0.133 0.119 0.887
11⁄4 1.277 1.223 17⁄8 27⁄32 31⁄4 0.308 0.133 0.119 1.012
13⁄8 1.404 1.346 21⁄16 29⁄32 3 0.333 0.143 0.128 1.119
11⁄2 1.531 1.469 21⁄4 1 3 0.333 0.143 0.128 1.244

Dimensions per ASME B18.2.1 1996