ACME and Trapezoidal Lead Screws
The single-start ACME thread is the most common form of the lead screw nut in North America. Developed in the mid-1800s, they can be
found on all types of machines, and are most suited to low-cycle or positioning applications. Their trapezoidal shape makes them better suited for the axial loading found in power transmission applications.
Standards for single-start ACME nuts apply to the inner thread dimensions. ACME lead screws are called out by their diameter, and then the threads-per-inch (TPI). For example:
A ¾-20 ACME has a major ID of 0.75” and 20 TPI
To calculate the lead (linear travel in inches per one screw revolution) simply divide 1 inch by the TPI. In the above example a 20-TPI nut will travel 0.05” per one revolution.