What is 1/8 NPT Tap Drill Size

1-8 pipe hole

There are a number of different types of drill sizes, and it can be confusing to know which one to use for what project. In this blog post, we’ll be discussing the 1/8 NPT tap drill size. This is a standard size that is often used for various projects. We’ll go over what exactly this size is and how to best use it. With this knowledge, you’ll be able to tackle your next drilling project with confidence.

What is the 1/8 NPT Tap Drill Size?

The 1/8 NPT tap drill size is used for tapping threads on an internal pipe, and it is a common size for home improvement projects. The NPT designation stands for National Pipe Thread, and it is the standard thread used in the United States [1]. The 1/8 NPT size is a smaller version of the standard NPT size, and it is often used for piping that carries fluids under high pressure. 

1-8 NPT port

When selecting a tap drill size, it is important to consider the type of material being tapped, as well as the thickness of the material. For example, a softer material like aluminum may require a larger tap drill size than a harder material like steel. In general, it is always best to err on the side of a larger tap drill size to avoid damaging the material.

What Size Drill Bit Do You Need for a 1/8 NPT Tap?

When it comes to threading, creating the perfect seal starts with having the right-size drill bit. This is especially true when working with taps, which are used to create screw threads. Taps come in a variety of sizes, and the size of the tap will dictate the size of the drill bit you need to use. For example, if you have a 1/8” NPT pipe tap, the R type is the appropriate drill bit to use with this tap. 

If the pipe tap is tapered, the ideal drill size is 21/64mm in fraction form or 0.339”. For non-tapered or straight pipe taps, use a drill size of 11/32mm or 0.344”. This delivers 27 threads per inch. With the right-size drill bit, you’ll be able to create a stronger, more secure connection.


The 1/8 NPT tap drill size is the diameter of the hole that needs to be drilled in order to install a 1/8 NPT threaded fitting. This size is typically used for light-duty applications, such as faucets, valves, or hose nozzles. If you’re not sure what size your threading needs to be, there are several online calculators that can help you determine the correct size.

Leave a Comment

Your email address will not be published. Required fields are marked *