What is the drill size for a 3/8 bolt? (Size Guide)

Content

What is the size of the drill for a bolt with a tightening of 3/8 - getting started
How to choose the right pilot hole drill?
What is a perfect match?

In this article, I will help you determine the correct drill size for your 3/8 tie bolt.

Pilot holes are required to get started with tapping or tapping screws. As a contractor, I needed the right drill bits to pre-drill holes for installing self-tapping screws or tie bolts because using the right drill will help you get the tie bolt firmly into whatever material you are drilling.

As a rule of thumb, for a 3/8 lag bolt, use a 21/64" drill bit to make the pilot hole. Using a drill, you should get a pilot hole size of 0.3281 inches.

Check out the detailed explanation and illustration below.

What is the size of the drill for a bolt with a tightening of 3/8 - getting started

To install the tie bolt, first drill a pilot hole with a drill bit. For a 3/8 lag bolt, use a 21/64" drill bit to make a pilot hole - you should end up with a pilot hole size of 0.3281".

It is very important. If you use a smaller or larger drill bit to make the pilot hole, the tie bolt will not fit snugly into the hole. You will have to re-drill another hole or change the material.

The type of drill also matters depending on the wood you are drilling. For example, hardwoods such as mahogany require well-fitting drills, while softwoods such as cypress can be drilled with a regular drill. (1)

However, a drill is not required for self-tapping screws. They can drill their own pilot holes as they move through the material. Drills are required for other tapping, tapping, tapping or thread rolling screws.

How to choose the right pilot hole drill?

Lucky for you, I have a simple trick to help you choose the right size drill from your drill set. You don't need to understand any specific drill bit concept or drill bit chat analysis to use this trick.

Follow these simple steps to select an accurate drill bit for drilling a 3/8 bolt hole.

Step 1: Get a set of drill bits and a tightening bolt

Keep a drill set and a 3/8 tie bolt side by side. Go ahead and describe with a pencil, pen or marker the place where you want to drive the bolt.

Step 2: Align the largest drill over the tie bolt

Now raise the 3/8 bolt close to your eye level and take the largest drill from the drill set. (2)

Align the drill bit with the lag bolt, placing it horizontally on top of the 3/8 tie bolt - the drill should rest on top of the 3/8 lag bolt.

Step 3: View the threads of the lag bolt perpendicularly

Position your head well and look at the threads of the tie bolt.

If the thread is partially or completely blocked, move on to the next, second largest drill. Align it over the 3/8 lag bolt and check thread behavior.

Step 4: Repeat steps one through three

Continue aligning the bits progressively from larger to smaller until you find the perfect match.

What is a perfect match?

If the drill does not cover the tie bolt threads and expose the tie bolt shaft/frame, then this is the ideal drill size for drilling the tie bolt pilot hole. In other words, the drill should drill with the shank of your lag bolt 3/8 in.

Once you have the right size drill, you can pre-drill a hole for the tie bolt. I reiterate that you should not use a drill bit that is too small or too large to cut a pilot hole for the tie bolt; the bolt will not fit and the connection will be loose.

Take a look at some of our articles below.