Thread cutting

Tools

Threads are either cut externally to the diameter of pipe (conduit) or rod, or internally to a drilled hole.

External threads

External threads are cut with stock and die. The die is the cutting tool which is available in a range of sizes and thread types. The stock is the handle used to turn the die.

When cutting an external thread, the size of the material must match the size of the die. A 10mm (eg 10M x 1.5) die must be used with 10mm outside diameter pipe or rod.

Stock

 

Internal threads

Internal threads are cut with tap and wrench. The tap is the cutting tool, also available in a range of sizes and thread types. The wrench is the handle used to turn the die and is available in two types: bar handle and tee handle.

When using a tap to cut a thread it is important to drill the correct size hole for the particular thread that is being cut, eg a 24mm thread (eg 24M x 3) requires a 21mm diameter hole. If the hole is drilled too large then there will be insufficient thread so that a bolt or pipe would pull out of the thread. If the hole is too small then the tap will break.