3/8″ Tap Drill Size

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You know, I’ve been there – trying to figure out which drill bit to use can be a real headache. I’ve even messed up a project once just because I had the wrong size! But if you’re wondering about the best drill bit for a 3/8 tap drill size, you’re in luck. I’ve got you covered.

What are the Drill Bit Sizes for a 3/8" Tap?

A 37/64″ drill bit is needed for a 3/8″ NPT tap.

NPT Tap SizeDrill Bit Size

How Tap Sizing Works for 3/8"

To fit the drill bits (shown in our chart), which are six inches long, you specifically need a 3/8″ NPT Tap and Drill. You also have to remember that 3/8″-16 Tap and 3/8″-24 are not the same thread pitches.

You can utilize e 3/8″ NPT tap in various DIY projects. If you intend to utilize screws or bolts, you can use a 3/8″ NPT tap to drill pilot holes. The material you use can affect how well you can drill them.

Tap Drill bits

A hammer drill is ideal for drilling into concrete and other hard materials. Cordless or corded drills can be used if you’re working with wood. Consider a corded drill if you need extra power.

You’ll need to be extremely careful when drilling a pilot hole in wood. Don’t split the wood while you’re at it! You’ll need a pilot hole to fasten two pieces of hardwood together.

Calculating the Tap Drill Size for 3/8"

The first step is to determine the size of your drill bit. It’s a straightforward procedure that does involve some mental math. Take the tap’s diameter [1] into consideration.

When determining a thread pitch to utilize, you need to consider the diameter of the drill. It doesn’t matter which one you choose, but you should choose the one that best matches your desired outcome.

Compared to a 24-inch tap, a 16-inch tap cannot generate as many threads. For the second time, you’ll want to pick a size that’s most comfortable for you. The drill bits you’ll need will depend on whether you’re using either.

tapping hole

When utilizing a 3/8″-16 tap, you need at least a 5/16″ drill bit. For a 3/8″-24 tap, a Letter Q or 21/64-inch drill bit is required.

Despite variations in taps and thread pitches, there is minimal difference in diameter. When it comes to drilling bit sizes, even the slightest distinctions can have a significant impact.

Why Do 16" And 24" Taps Require Different Sizing?

With so many options, knowing which is best for your application. They are still both sized the same way. When comparing the two, pay attention to their thread counts.

Your project will suffer if you use a drill bit that doesn’t fit correctly. Use the chart to determine which 3/8″-16 or 3/8″-24 you should use or prefer. If you need a complete size chart of tap drills, you can check this guide.

Drill Bit Size for 8-32 Taps

Use some scrap material to test if 3/8″-16 or 3/8″-24 works for your project. Preparation is preferable to winging it when it comes to a project.

It all boils down to the type of drill bit you desire. You must consider even the smallest details to get the intended outcome. You may want to drill holes and test before you get started on your project.

You can experiment by switching out the appropriate drill bits to determine which holes produce the required results. Your actual work can begin after deciding what you need between 3/8″-16 and 3/8″-24.


If you’re looking for a drill bit for a 3/8″ tap, there are quite a few that can fit the bill. To find the best one, just think about how long you want the thread to be. 

And trust me, once you pick the right drill bit, it’ll work wonders with different materials. Just make sure to match it with the right tools.

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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