What Is a Thread Die – And How to Use It for External Threading?

What is a Thread Die?

A thread die is a tool used to cut external threads on rods, bolts, or pipes. It works by shaping the outer surface of a cylindrical object into a helical groove—forming a threaded profile that matches nuts or tapped holes.

Unlike taps (which cut internal threads), dies are used for external threading. See below for comparison:

Structure of a Thread Die Holder

A thread die is typically mounted in a die stock (holder), which helps maintain alignment and torque during operation. Let's take a closer look:

Fastening Screws – Lock the die into place securely
Positioning Groove – Ensures correct alignment of the die teeth with the rod
Round Die – Interchangeable cutting component made of high-speed steel or alloy steel

How to Use a Thread Die

Chamfer the Rod End: Use a file to slightly taper the end of the rod.
Secure the Die: Place the die into the holder, aligning the groove with the set screw.
Apply Cutting Oil: Reduces friction and increases die life.
Start Threading: Apply gentle pressure and turn the holder clockwise.
Back Off Frequently: Every 1–2 turns, reverse slightly to break chips.
Clean and Inspect: Brush off chips and test thread fit with a nut.