Lag Bolt Pilot Hole Size
The best way to choose the right drill bit for a lag bolt is to visually inspect it. Hold the screw up to the light and compare it with a standard drill bit. If the drill bit diameter covers the screw shank but does not show the threads, you have found the correct size drill for your lag bolt. This method is quick and easy to use in the field and works well even with a dark or dull screw.
Lag screws, also known as hex lag screws or coach screws, are thread-forming fasteners that secure two pieces of material together by creating their own mating threads as they’re installed, without weakening the materials being joined. They’re used for fastening wood to other types of wood, metal, concrete and more.
While lag bolts are very strong, they can be difficult to install if the proper hole size is not used. Drilling a hole that’s too small will create a weak spot in the wood, while drilling a hole that’s too large can cause the screw to penetrate deeper than necessary.
Using a drill bit that matches the root diameter of your lag bolt ensures that you’re drilling a hole of the same thickness as the screw. This will help you get the most strength and security out of your lag bolt and prevent it from loosening over time. The table below shows recommended hole sizes for a variety of different lag bolts and lengths. pilot hole for 1/4 lag screw