What Size Drill Bit for a 3/8″ Tap

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Finding information about which drill bit you need can be a challenge. But if you need to know what size drill bit you need for a ⅜” NPT tap, then you’re in the right place. I’ll answer this question shortly.

In this guide, I’ll also talk about the other factors that you need to consider when using a drill bit for a ⅜” NPT. You want to make sure that you want to drill the perfect holes before installing nails or screws. Anything less than that and your project may not go as according to plan as you thought.

With that said, let’s take a look now at the answer to the million-dollar question.

What Size Drill Bit for ⅜” Tap?

A ⅜” NPT tap requires a 37/64” diameter drill bit.

NPT tap sizeDrill bit size

Now that you have all the numbers, you will also need a ⅜” NPT Tap and Drill set in order to accommodate the drill bit you’ll need. The length of these drill bits is usually six inches in length.

A close-up image of a drill bit

There are also two different thread pitches that you need to be aware of. These include ⅜”-16 Tap and ⅜”-24 Tap. As you will notice below, each of them has its own corresponding drill bit sizes.

If you need to decide which is best, keep reading to find out more.

Tap sizeDrill bit size

How to Use ⅜” NPT Tap?

First and foremost, you want to make sure what your drill size is. It’s a simple process that does involve a bit of number crunching. Measure the diameter of the tap.

The measurement of the drill is part of a formula that you need to crunch together to determine which thread pitch you’ll want to use. It really doesn’t matter, but you’ll want to choose one that will best match your desired result.

Keep in mind that a 16-inch tap may not produce a lot of threads compared to a 24-inch tap. Once again, you’ll want to choose the size that fits you best. If you are using either or, you’ll want to be aware of the size of the drill bits you’ll want to use.

For example, if you are using a ⅜”-16 tap then you’ll want the drill bit to be around 5/16”. For a ⅜”-24 tap, you’ll need a drill bit measured at 21/64″ (Note: the letter drill bit is Q). If you are using a ⅝” tap requires a bit size of 17/32”.

Despite the taps and thread pitches being different, there really isn’t much change in terms of the diameter. It’s the little minute details that will make the difference between one drill bit size and another.

When to Use ⅜” NPT Tap?

The ⅜” NPT tap can be used for multiple DIY projects. If you are planning on applying bolts or screws, you can use a ⅜” NPT tap to drill pilot holes. Drilling them may depend on the kind of material you are using.

If you are using a hammer drill, it will be perfect for drilling concrete or similar materials. If you are using wood, you can consider using either a cordless or corded drill. Obviously, if you need more power, consider a corded drill.

With wood, you’ll want to be really careful when drilling a pilot hole. Make sure you’re not splitting the wood while doing this. If using hardwoods, a pilot hole is essential if you are fasting two pieces of them together.

An image of drill bit set

If you are using softwoods, pilot holes may not be required. However, it’s highly recommended that you drill one if you are planning on fastening them with nails, screws, or bolts.

It can also be used to re-thread carbon steel pipes that are either jammed or have been damaged. So if you are working any kind of piping or metal, using a ⅜” NPT tap will be ideal.

Other Considerations for ⅜” NPT Tap

You may be stuck determining whether or not a ⅜”-16 tap may be the best option or its 24 tap counterpart. Keep in mind they are measured the same in terms of diameter. What sets them apart is the number of threads per inch.

A not so perfectly fit drill bit will not go well for your project. Consult with the chart above on which drill bit you need to go with depending on your choice between ⅜”-16 or ⅜”-24.

If you have scrap material handy, you can use it for small test projects to ensure if ⅜”-16 or 24 is the best option for you. It’s better to prepare for the project before flying blind and winging it.

Before Using a ⅜” NPT Tap

Before you start using a ⅜” NPT, not the ¼” NPT with a bit size of 7/16″, it’s important to know what kind of material you plan on working with. Some materials like metal or concrete will require a different kind of drill (i.e – a hammer drill).

It all comes down to which drill bit size you want. The smallest of details can make the difference between the desired result you want and something that may miss the mark. Before you start your project, you can try and drill a few test holes.

You may have ⅜”-16 and 24 threads. Switch out the corresponding drill bits and see which holes match your desired results. Once you choose which thread is best, you can use it for the real deal.

The image of what size drill bit for a 3/8 tap


There are a few drill bit sizes that you can use with a ⅜” NPT tap. Choosing the right thread length will help you decide the best option. These drill bits are great for multiple types of material, so be sure to use them with the other required tools.

I hope this guide has been helpful. Finding bits for a ⅜” NPT tap doesn’t necessarily have to be a challenge. But now that you know what to look for, you can purchase a few of your own for all your home improvement projects.