Lag Bolt Pilot Hole Size
Like other screw-in fasteners, lag bolts require pilot holes to be installed properly. The correct drill bit sizes depend on the specific lag bolt size and wood species. Pilot hole sizes also vary depending on the length of the lag bolt and the materials it will be joining together, but there is generally a recommended diameter range. For this reason, it is important to consult the documentation included with a specific lag bolt and hardware to ensure proper installation.
What Is a Lag Screw?
Unlike standard wood screws, which cut their own holes as they’re screwed in, lag bolts are hex- or square-shaped and threaded along their entire length. Their larger heads allow them to take a greater load than a wood screw and exert more force, which can help prevent a fastener from loosening over time.
Often used in structural applications, lag bolts are intended to be driven at least two inches into the material they’re connecting together for optimal strength and durability. To do so, it’s important to pre-drill the necessary holes to ensure a solid connection.
To determine a suitable drill bit for a particular lag bolt, simply take the head off of the bolt and compare the drill bit to its core (without the threads). The diameter of the core should match the diameter of the hex or square head. For the threaded section, the diameter of the hex or square should be 75-80% of the bolt’s overall diameter. The exact diameter required will vary based on wood density, but a general guideline is suggested in the table below for both soft and hardwoods. pilot hole for 3/8 lag screw