Leads Screws – Terms & Definitions
By Zoe Moser (Edited by Kevin Wright and Shizu Yamaguchi)
How do you determine the core diameter of a lead screw? What exactly is the pitch diameter? What are some important terms to know about lead screws?
We have summarized basic terms and designations relating to lead screws below.
First, let’s look at the drawing of a lead screw. The individual terms are explained in detail below.
Outer diameter:
The distance between the outermost edges of the lead screw flanks is called the outer diameter, i.e., it is the largest possible diameter of the lead screw. The outer diameter is also known as the nominal diameter.
Core diameter:
The distance between the base of the lead screw, i.e., the lowest point, and the opposite base of the lead screw gives the core diameter. This means it is the smallest diameter on the lead screw. The core diameter is important as it controls what machining and features can be added to the lead screw, i.e., tapped holes.
Pitch diameter:
The distance perpendicular to the axis between two opposite flanks, or the space between the profile centre lines, is called the pitch diameter.
Lead screw flank:
The flank results from the extension of the line from the lead screw base to the tooth flanks or to the end of the profile centre line.
Flank angle:
The flank angle is present on all lead screws. It describes the angle from one flank of the lead screw to the next.
Pitch:
The “lead” of a lead screw is also termed “pitch”. It describes the distance between two adjacent and parallel flanks, measured parallel to the axis, between two adjacent and parallel flanks of the same lead screw. The pitch indicates the linear travel per 1 revolution of the lead screw.
A metric or trapezoidal lead screw will have a small pitch, resulting in shorter linear travel distance per revolution. High helix lead screws will have a larger pitch that can convert a single rotation into a longer travel distance. Shop for our dryspin high helix lead screw technology here.
Turn of a thread:
The full circumference of the helical curve of a lead screw is called the turn of the thread.
