Are you wondering what size drill bit to use for a 1/8-27 NPT tap? If so, you’re in the right place. 

In this blog post, we will discuss what size drill bit for a 1/8-27 NPT tap and what is the tap drill diameter for a 1/8-27 NPT pipe thread. We will also look at how to determine the tap drill size.

What Size of Drill Bit for 1/8-27 NPT Tap

When it comes to determining the size of the drill bit for a 1/8-27 NPT tap, it depends on the type of tap you are using. Generally speaking, a standard tap requires a 7/16-inch drill bit. However, if you’re using a bottoming tap, you’ll need a 1/4-inch drill bit.

What is the Tap Drill Diameter of a 1/8-27 NPT Pipe Thread?

The tap drill diameter for a 1/8-27 NPT pipe thread is 0.265 inches. This means that you need a drill bit that is 0.265 inches in diameter to create the correct thread size. To give you an example, if you were to use a 7/16-inch drill bit, it would create a thread that is slightly too large.

How Do I Determine a Tap Drill’s Size?

Determining the tap drill size is a simple process. All you need to do is measure the outside diameter (OD) of the thread you are trying to create. For example, if you are trying to create a 1/8-27 NPT thread, then the OD is 0.265 inches. 

Once you have the OD, you can then subtract the thread pitch (TP) from the OD. For a 1/8-27 NPT thread, the TP is 0.0315 inches. Therefore, the tap drill size is 0.265 – 0.0315 = 0.2335 inches.

What Hole Size Do I Drill for a 1/8 NPT Tap?

A 1/8 NPT tap requires a drill bit size that is slightly smaller than the major diameter of the thread. The major diameter of a 1/8 NPT thread is 0.3345 inches, so you should use a drill bit with a diameter of 0.3125 inches (5/16″). 

It is important to note that the drill bit size must be smaller than the major diameter of the thread in order to create the correct thread size. If the drill bit is too large, the thread will be too small and it will not be able to create a proper seal.

Conclusion

In conclusion, the size of the drill bit for a 1/8-27 NPT tap depends on the type of tap you are using. For a standard tap, you will need a 7/16-inch drill bit, and for a bottoming tap, you will need a 1/4-inch drill bit. 

The tap drill diameter for a 1/8-27 NPT pipe thread is 0.265 inches. To determine the tap drill size, all you need to do is subtract the thread pitch (TP) from the outside diameter (OD). Hopefully, this blog post has been helpful in answering your questions about what size drill bit for a 1/8-27 NPT tap.