Table of Contents
The above chart is for single start threads where the lead equals the pitch (L=D). The lead of the screw equals its pitch times the number of starts (L=nXP). Therefore Multi start threads have large lead angles.
Screw Lead Angle Formula
The lead angle is measured at the pitch diameter. It can be represented by a right triangle whose base is the circumference of the screw, and its height is the lead of the screw.
- n – Number of starts
- P – Pitch of the thread (Inch / mm)
- d2 –Pitch Diameter of the thread (Inch / mm)
Lead Angle Calculator
For easier thread selection and higher accuracy, use the ThreaDoctor calculator.
As machining people, why do we care about the lead angle?
When turning a thread with a typical laydown insert, the best practice is to tilt it by the lead angle size. It ensures symmetrical relief on both sides of the insert flanks.
All threading tools suppliers provide an assortment of shims to tilt the inserts to all the needed angles. They will also publish charts that specify the correct shim for each thread.