# What Size Drill Bit for 5/16 Tapcon?

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Tapcon bolts are designed to function optimally with specific drill bits; using the wrong-sized drill bit is ineffective and dangerous. Being an experienced handyman, I can help you avoid confusion when selecting the drill bit for 5 16 Tapcon.

In general, the fittest overall size drill bit for the 5 16′′-18 tap is a 17 64′′ drill bit, which is also known as an F drill bit. Despite both being 5 16′′ taps, they have varying lengths and thread pitch dimensions. Because of the varying dimensions, the taps necessitate the use of different-sized drill bits.

I will cover more detail below.

## What Size Drill Bit Should You Use for a 5/16′′ Tapcon?

The fittest overall size drill bit for the 5 16′′-18 tap is a 17 64′′ drill bit, also known as an F drill bit.

Knowing the sizing variations is the first step in determining what size drill bit you require for a 5 16′′ Tapcon.

When discussing the 5 16′′ tap, remember that there are different measuring variations an 18-tap and a 24-tap.

Despite both being 5 16′′ taps, they have varying lengths and thread pitch dimensions. Because of the varying dimensions, the taps necessitate the use of different-sized drill bits.

Check the tap’s specific length or thread pitch to determine what size drill bit you require for your 5-16 tap. You can then figure out which drill bit to use.

## Before You Start Drilling

Calculate Tap Drill Size for 5/16″

You only require a basic mathematical understanding and the size tap you will use, the 5 16′′ tap, to compute your tap drill size.

First, obtain the diameter of the tap.

You can measure the diameter of the Tapcon physically or check to the 1st number in the tap’s specifications.

Example. The diameter of the 18″ and 24 5/16′′ taps is 5 16′′ (.3125).

Once you’ve determined the diameter, plug it into the equation DH=DMB -.0130(% of full thread desired/Ni). Don’t be concerned if this formula appears complicated.

The DMB is the diameter measurement you calculated earlier,.3125.

The complete thread percentage varies depending on the size of thread you want, but we’ll use 75.

The other variable, Ni, represents the other side of the tap. Let’s take the 5 16′′-18 tap as an example. The tapcon has a Ni of 18.

Input the 5 16′′-18 tap numbers into the formula to get:

DH = 0.3125 – 0.0130

Then compute DH. You should get something like 0.2583, which you can round up to the nearest drill bit size. For our purposes, the closest drill bit size to the 5 16′′-18 tap is 17/64 which corresponds to an F drill bit.

You are now familiar with the basics of 5 16′′ tap measurements, and you can put your knowledge to use. Just ensure you understand which size you have—the 5/16-18″ or the 5/16-24″—because they have varying compatible drill bit sizes. After sorting that out, it’s time to get to work.

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