What Size Drill Bit for 1 8 NPT Tap


Are you in search of the right drill bit for threading a 1/8 NPT (National Pipe Thread) tap into a hole, but uncertain about the appropriate choice? Rest assured, this article aims to provide you with insights on determining the ideal drill bit size for a 1/8 NPT tap and the significance of this choice. Moreover, you’ll possess the knowledge and confidence to successfully undertake your threading projects

What Size Drill Bit for 1/8 NPT Tap: The Golden Rule

When you are referring to the American National Standard Taper Pipe Thread, it is advisable to use a drill size represented as Q, which is equivalent to 0.332 inches or 8.43 millimeters in numerical terms.

How to Select Drill Bit for NPT Tap

The following table encompasses all the common tap and die sizes and their corresponding drill bit sizes available in the market, making it a handy reference to keep.

what size drill bit for 1/8 NPT tap

Diverse Drill Bits Transform Your Threading Experience

High quality drill bits can significantly optimize your threading or overall work process and experience, making it indispensable. The quality of a drill bit is determined by several factors, including material, coating, and design, which affect its heat resistance, hardness, and durability. Common drill bit materials include High-speed steel and cobalt, while coatings like TiAlN (Titanium Aluminum Nitride), Black Oxide (BlkOx), and TiN (Titanium Nitride) further impact performance.

You can find detailed comparative tests in the following link:

High-Speed VS Cobalt & TiAlN, Black Oxide and TiN comparison

FAQs: Your Burning Questions Answered

Q1: What is the 1/8 NPT tap used for?

A1: The 1/8 NPT tap is commonly used for creating threads in pipes or fittings with a nominal pipe size of 1/8 inch. It’s a standard size for various plumbing and industrial applications.

Q2: Can I use a regular drill bit for tapping NPT threads?

A2: While you can use a regular drill bit, it’s recommended to use a bit that matches the tap size to ensure precision and quality threads.

Q3: What happens if I use the wrong-sized drill bit for tapping?

A3: Using the wrong-sized drill bit can lead to loose connections, leaks, or damaged threads. It’s crucial to match the drill bit size to the tap for a secure fit.

Q4: Should I lubricate the drill bit when tapping NPT threads?

A4: Yes, using cutting oil or lubricant is advisable when tapping NPT threads. It reduces friction, heat, and prolongs the life of your tap.

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