Lag Bolt Pilot Hole Size
If you’re a homeowner doing major construction, you’re likely familiar with the use of lag screws. These heavy-duty fasteners are much stronger than standard wood screws, and they have a specific purpose – to connect and secure two pieces of wood together.

But they can be difficult to install if you’re not using the right tools and techniques. One such technique is the proper use of a drill bit to create a pilot hole before driving the screw in place. The wrong size drill bit can ruin the threads of the screw and cause it to strip or break prematurely.

The article that follows will explain how to select the correct drill bit for a given lag bolt. We’ll also provide an easy-to-follow chart that helps you identify the optimum pilot hole sizes for a wide range of lag screw diameters and lengths.

As a general rule, the lag bolt should penetrate at least twice as deep as the thickness of the material it’s being used to secure. This allows the hex head to fully engage into the attached piece of wood and provides adequate strength for the fastening process. The exact amount of penetration required will vary based on the species and age of the wood, so some experimentation might be necessary when working with new materials. For example, a lag screw that’s being installed in a new Douglas fir stud should be driven about 3 inches into the stud to ensure a strong fastening. pilot hole for 3/8 lag screw