Lead screws – terms and definitions

Zoe Moser | 16. October 2020

The most important terms and designations concerning lead screws

How do I actually recognise the core diameter? What exactly is the pitch diameter? What are the terms I need to know about lead screws?

We have summarised the basic terms and designations relating to lead screws simply and clearly. 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 opposite lead screw flanks is called the lead screw outer diameter, i.e. it is the largest possible diameter on 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.

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 other.

Pitch:
The “lead” of a lead screw is also termed “pitch”. It describes the distance, measured parallel to the axis, between two adjacent and parallel flanks of the same lead screw. It indicates in mm the linear travel per revolution of the lead screw.
 
In contrast to a metric or a trapezoidal lead screw, the high helix lead screw has a high pitch. The high helix lead screw can convert a small radial movement into a relatively large axial movement with one revolution. Learn more about 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.  

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