Sporting a rustic look, square lag screws are often used in wood construction as well as ordered for aesthetic purposes. These screws are more readily available as a standard stock item in the marketplace.

Manufacturing

Baseline Bolt manufactures a range of square lag screws of diameter 1/2″ - 1-1/2″ in most of the ASTM, AASHTO & SAE specifications. Moreover, it is possible to create special tooling to produce nonstandard bold heads or head dimensions with the name and/or logo of your company.

If not specified, the nonstandard lag screws that are manufactured by Baseline Bolt will have a semi-cone point instead of a gimlet or a cone point. It is important to have a full point because a pilot hole that is as big as the lag screw’s root diameter has to be drilled before installation. Besides, for small diameter screws, a gimlet point is also designed so that installation without a pilot hole is possible. Lag screws in above listed diameters don’t generally require a gimlet point because too much torque is required for installing large screws without having to drill a pilot hole first. If there isn’t a pilot hole, heads of the screws tend to break often prior to the proper installation of the lag.

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

Click table to show drawing
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