Examples and Terminology - Lathe Mill

TPI - Threads per inch define the number of times a thread traverses the circumference of a rod over 1 inch measured down the length of the threaded rod. It also describes how many times a nut travelling along the threaded rod must be turned to travel 1 inch down the rod.

PITCH - Pitch of a thread describes the distance a thread travels down a rod with one turn. Thus a rod with 5 tpi will have 5 threads per inch or a pitch of 1/5th of an inch or 0.2 inches.

LEAD - The lead of thread measures how far the thread travels in one turn down the rod. A single thread had a lead equal to pitch. Multi-thread have a lead which is a multiple of the pitch depending on how many starts have occurred. A double-thread has 2 threads created which are placed between each other. In this case the pitch is double that found in a single thread and the lead is equal to 2 times the pitch. If we were to follow one of the threads around the circumference the lead would be the distance between the beginning and end of the turn as measured down the length of the rod.

MULTI-THREAD- A multi -thread operation places 2 or more threads along a rod using 2 or more starts. The multi-thread has the advantage of causing a nut to travel farther in one turn than a single thread. A double thread with a pitch of 0.2 inches or a 5 tpi would have a lead of 0.4 inches. The nut would travel 1 inch with 5 turns in a single thread and 2 inches with 5 turns in a double thread. Some rope designs use the multi-thread operation and this is its relevance. An example of a double threaded rope is shown above. It was made with 2 starts (see below).

STARTS - A start is the process of placing a thread from the beginning of the rod by turning the rod and placing another thread between the previous thread. See multi-thread above. See the quad thread below.