What Size Of Drill Bit Should Be Used For A 3/8-16 Tap?

Finding the correct drill size is challenging. The several options available in the market make it challenging to find the correct one. Looking for the correct one in a hardware store is overwhelming. You can find plenty of home improvement items there.

You scan through your checklist and find the tap and drill bit. These items may be new to you. This article is specific to finding the best fitting bit for the 3/8 tap drill, so you will not find it too challenging.

We also thought of adding sections that provide more information about related topics, such as what to consider before drilling and how to drill.


For a 3/8-16″ tap, the best drill bit size is 5/16″. When you know the exact measurements, you can avoid many issues in the future. For other tap sizes, they are as follows:

  • 37/64″ drill bit size for a 3/8″ tap size
  • 21/64″ drill bit size for a 3/8″-24 tap size

Table of Contents

What is tap drill size?

Defining the definition of tap drill is important in understanding the topic. You will encounter this term several times, so getting a firm grasp of its meaning will go a long way. In simpler terms, we use a tap drill to cut a cylindrical opening in stock, typically a metal material. The process involves creating threads inside so it can accept a screw.

The tap is a hard metallic cylinder with thread. You insert it into the tap drill’s hole, forming the female part of the mating pair. On the other hand, the male part is a bolt or a screw. Manufacturers use a specialized die to cut the threads into metal cylinders. We call this process threading.

Humans have long used nuts, screws, and bolts to fasten two or more parts together. The industry has recognized it as a global standard since the middle ages. Modern fasteners usually utilize metal, but earlier ones use wood because it is easier to acquire.

The size will increase as the load increases. In other words, the fasteners are thicker if it requires supporting heavier items. Windmills and ships require larger fasteners than a table, for instance. The mating components are the tools these craftsmen use are usually handmade.

A tap drill uses a hardened bit to cut holes through metals in a modern machine shop. The most important factor to consider in the size selection is ensuring accurate measurements. Removing all the extra metal until little to none is left is ideal. Extras may significantly increase stress or tension, resulting in imbalances.

We size the tap drill by its diameter and length. The hole we drink is countersunk, making it slightly wider on the top. The countersink enables the accommodation of the tap, tapering through its tip. 

Drill bit size for a 3/8″ tap

Avoid guessing the size you need for a tap. Knowing the exact measurements is important to avoid issues from arising in the future. The thread count dictates the size of the drill. A 3/8″-16 thread requires a 5/16″, while a 3/8″-24 requires a 21/64″.

We recommend referring to the table below for the measurements. It will be useful in the future if you are looking for the correct size.

Drill Bit Size

Drill Bit SizeNPT Tap Size

Best drill bits for a 3/8 tap

Some people prefer a curated list of recommended products. The following items below are the best drill bits for a 3/8 tap. These are all Amazon products, so you will only have to look in one place.

DEWALT Drill Tap, UNC, 3/8-Inch

The Dewalt 3/8-inch combines drill and tap bits, allowing a single application for all holes. You can countersink and deburr in one step, saving you time and effort in the long run. The hex shank’s design is for impact drivers, and the speed tip allows drilling.

The Dewalt can withstand extreme job conditions, making it an excellent option for construction and building needs. Do note its country of origin is China and may come in odd colors. The material is also a blend of different metals.

Before purchasing this item, we recommend checking and ensuring compatibility. When you get confirmation of its compatibility, we advise getting two or more pieces of the same size for backup purposes.

Item Dimensions LxWxH1.87 x 0.25 x 5.75 inches
Item Weight‎0.634 ounces
Surface Recommendation‎Alloy Steel
Tool Flute TypeSpiral


  • We always love Dewalt products.
  • The best way to do it is to use an impact driver.
  • They worked great when we tried them.
  • When used correctly, they provide great durability.


  • People that didn’t follow the instructions saw that they’d tend to break.
259 Reviews
We trust DEWALT.

3/8-Inch Carbon Steel NPT Pipe Tap

Drill America uses carbon steel pipe, making it excellent and clean. It uses a black oxide drill bit suitable for the maintenance and production of drilling jobs.

This pipe tap is compatible with different surface applications, such as metal, plastic, and wood. It is about six inches long and has a round with square shank type.

What is the importance of black oxide? It provides toughness and hardness for wear resistance, making it excellent for most general-purpose applications.

The treatment also adds lubricity to the application. It also creates small pockets on the tool’s surface, acting as a container for the coolant.

These are available in several sizes, so we recommend checking the product page for the most recent offerings.

NamePOU3/8NPTW/DRILL 3/8″ Carbon Steel NPT Pipe Tap
BrandDrill America
Finish TypeUncoated
Item Dimensions LxWxH6 x 4 x 2 inches
MaterialCarbon Steel
Shank TypeRound with Square
Weight8.16 Ounces


  • They come from a popular vendor.
  • We tried them on cast iron with great success.
  • We love that it works for high speeds.
  • It’s very durable.


  • As with other products, if not used correctly, they might get ruined.
Carbon Steel NPT Pipe Tap
2,789 Reviews
Carbon Steel NPT Pipe Tap
It's a solid product.

Amoolo 5/16″-3/8″ Brad Point Wood Drill Bits

The Amoolo 5/16″-3/8″ drill bit is excellent for woodworking needs. The parabolic double flute design improves chip evacuation, leading to a smooth finish on the hole’s surface.

You will notice the effect when drilling deep holes. The industry-standard high-speed steel provides heat resistance and wears resistance.

A speed-point tip provides self-centering support and fast drilling. You can also position it in several angles without issue.

The Amoolo brad point works for all wood types, including hardwood.


  • They worked great in the wood we tried them on.
  • They feel sturdy.
  • They’re true to size.


  • The seller is less popular than others.
  • We wish the storage case were better.
50 Reviews
It's a good budget option.

Comoware Combination Tap and Drill Set

The Comoware is a six-piece set containing the following thread tap drill bits – 1/8-inch, 5/32-inch, 3/16-inch, 1/4-inch, 5/16-inch, and 3/8-inch. The most common applications are tapping, countersinking a single bit, and drilling.

The metal’s surface has a coating that prevents corrosion. It also improves adhesion resistance, making the drill bit durable and long-lasting. The high-quality HSS 4241 material used for the bit enables fast cutting through hardwood material. It offers superior durability and cutting power.

A 1/4-inch hex shank fits through all power tools, so compatibility is not an issue. You can quickly lock and change the chuck with minimal effort. A self-centering design allows quick penetration. Lastly, the set includes a holder, allowing easy organization and storage. 


  • It’s a great set.
  • They’re sharp.
  • The price is very reasonable.
  • They cut clean.
  • We like the storage case.


  • Make sure to use oil.
257 Reviews
COMOWARE will get the job done.

DWT54582 3/8″-16 UNC High-Speed Steel

The Drill America taper-style bit starts the thread square with the workpiece. We recommend using it with a high-speed hand tap. They are popular for CNC or general machine tapping. There is no additional treatment or coating with this bit.


  • There are many options available on Amazon.
  • Drill America is a reputable store.
  • It’s better than some of the cheaper options we tried.
  • It worked great on the aluminum we tried it on.


  • Some people have received the wrong sizes.
High Speed Steel Taper Tap
1,507 Reviews
High Speed Steel Taper Tap
It works on a range of materials.

Hymnorq HSS 4341 Imperial 2-in-1 Combination Drill and Tap Bit Set

The Hymnorg Imperial 2-in-1 Set uses 4341 HSS for durability. Its top applications are wood, plastic, and soft metal, such as iron and aluminum.

A single-pass tap helps you save time and labor. The self-centering feature eliminates the need for center punching or drilling.

Wide flutes remove the chips from the hole. Alternatively, you can also use a multi-spindle head with a reverse mechanism. The set contains these six imperial sizes – 1/8-inch, 5/32-inch, 3/16-inch, 1/4-inch, 5/16-inch, and 3/8-inch.


  • It’s a cheap little set.
  • Make sure they provide enough depth for what you’re trying to do.


  • You’re not getting the highest quality bits out there.
  • They will not work on hardened steel.
579 Reviews
Here's a great set.

What to consider when drilling

man using a drill

Before you start doing work, we recommend reading through some guidelines. There are a few things worth considering when drilling.

  • Material
  • Size of the drill

You can proceed with drilling as soon as you find the correct material and tap of the drill size. We suggest using a scrap material first if you are unsure or if it is your first time. You may need to practice first to get the idea before tapping the actual piece.

We recommend using the correct thread percentage and bit size for your project. You should be able to avoid unnecessary errors and costs if you know what you need and how to work around it.

How to drill

drill bit

This section provides a high-level overview of how to drill. Start by gathering all the tools and materials you need for the project. Mount at least two clamps if working with a metal piece to avoid spinning and slipping. It should also prevent injury from happening.

Prepare and wear the necessary protection and safety equipment to stay clear of injuries and accidents. Goggles and gloves are the most typical protective wear you can use. Optionally, you can wear a long-sleeve shirt to protect your skin from debris.

Mark the area to drill using masking or painter’s tape if you already know it. Otherwise, locate first before marking anything. Ensure you have a solid foundation and support when working with thin or flexible material. It prevents slipping and deformation from occurring.

Position your tool at a 90-degree angle from the application surface. It will prevent issues from adding the screw.

A drill press is a big help when used with a handheld tool. We suggest keeping it clean and free from dirt after every use. It ensures the best resulting pilot holes and also prevents overheating. 

How to use 3/8 taps


Here is a step-by-step guide on how to use 3/8 taps.

  1. Create a threaded pilot hole, allowing a screw or bolt to slide in easily. It is almost impossible to get it inside without creating a pilot hole.
  2. Have the bolt and tap available for a visual comparison.
  3. Practice making a hole into a scrap material to know if you have the correct sizes.

These steps are also applicable to other tap sizes in the market. However, before applying exactly everything, we recommend researching prior to it. There might be slight differences in how to use a specific size.


The following are the frequently asked questions.

What size hole do I drill for a 1/4″ 20 tap?

You need to use drill bit #7 with a diameter of 0.203 inches or 13/64 inches. One size up or down may still work, but unlikely can provide the best fit.

What size hole do I drill for a 5/16 tap?

We recommend using a G or F drill. The sizes of these are 0.2610 inches and 0.2570 inches, respectively. 

What size hole do I drill for a 10/32 tap?

The correct size is a #21 drill bit for a 10/32 tap. It has a fractional equivalent of 5/32 inches. 

What is the next size up from a 5/8 drill bit?

The next size up is 11/16 inches.