3/8-16 Tap Drill Size

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When working with bolts, it’s important to pick the right tap size for a pilot hole. For sure, you want to get the correct 3/8-16 tap drill size for your home project; otherwise, things can go south. For this matter, I’ll break down the sizing table and give you some pointers on drilling a tap.

What Size of Drill Bit Do I Need for a 3/8-16 Tap?

A 3/8-16 tap should be used with a drill bit size of 5/16-inch. Here is a table below to help you with the 3/8-inch tap sizing.

Tap Size and PitchDrill Bit SizeFraction

The right drill bit size is very important in creating a pilot hole. If you drill a smaller hole, the tap could break and crack. 

If your drill hole is too large, then you will end up having weak threads. You will need to strip off your screw or tap while doing the project.

tap hole

Another thing to consider when you are using the 3/8″ tap is the thread percentage. You can choose between the 50% thread or the 75% thread. 

Look at the table below that shows the standard thread per inch and the drill size for the 50% and 75% threads.

Screw SizeMajor DiameterThreads Per Inch (TPI)75% Threads for Brass, Aluminum & Plastics50% Threads for Stainless, Iron & Steel
Drill SizeDecimal EquivalentDrill SizeDecimal Equivalent

Usually, the thread we use is the 75% drill. However, in some cases, you only need to use 50%. It depends on the material that you are working on. Working on harder material, such as steel [1], requires a tighter connection with bolts and screws.

tap drill sizes

Thin and soft materials usually need stronger threads and smaller holes. On the other hand, harder materials need a larger hole. It is because you only need to apply less pressure on the tap while cutting. 

You can check the details from the manufacturer to know their recommended thread percentage.

Considerations to Know When Drilling a 3/8" 16 Tap

Once you know the tap drill size and the material you will use, it is time to proceed with the drilling process. 

If you are not used to drilling the material you have, it is best to use a scrap piece to try the tap. Doing this will give you an idea of how you should tap on the real workpiece later.

Using the right thread percentage and drill bit size is crucial for achieving the best results in any project. Trust me, you’ll save time and money by just knowing what you need upfront. Here’s what else you should consider.

How to Start Drilling

Before beginning the drilling process, ensure you have gathered all the necessary materials and tools for the project. When drilling into a metal piece, use at least two clamps to secure it, reducing the risk of slipping, spinning, and potential injuries.

tapping with clamp

Wear necessary safety equipment, like gloves and goggles, to protect yourself. Mark the area to be drilled using a painter’s or masking tape. If drilling on a flexible or thin material, ensure that it has solid support to prevent deformation. 

Drill at 90 degrees to prevent problems when adding the screws. If you can, use a drill press for your handheld drill to guide you. Keep your drill bits clean and sharp to ensure getting the best pilot holes and to prevent them from overheating.

How to Properly Use 3/8" 16 Taps

To properly use 3/8″-16 taps, create a threaded pilot hole for a bolt or screw to get in easily. Getting the screw or bolt into the material is almost impossible without making a pilot hole. 

Before making the pilot hole, you should have both the tap and the bolt for a visual comparison.

tapping hole

To know whether you are using the right tap and screw, practice making a hole into a scrap material. 


This is a method that I use in tapping threads into a hole. It involves going into the material briefly and then backing off. Pecking prevents your drill bit and taps from overheating and breaking under extreme torque.

Pecking involves turning the tap for a full turn and then half turn out. You can also do a full turn to get the tap out of the hole safely and completely. It is a little more time-consuming but will give you even threads. 


Choosing the right 3/8-16 tap drill size can make a big difference to your project. It will save you from wasting resources and energy. It will also protect you from possible injuries. If you want to be sure which tap drill size to use, refer to the tables of tap drill sizes that I prepared for you.

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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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