Table of Contents
Definition of Screw Lead Angle
The lead angle (φ) measures the inclination of a screw helix from a plane that is perpendicular to the screw’s axis. In more simple words, it is the proportion between the screw’s lead and its diameter.
Lead/Diameter Chart
As seen in this chart, a screw with a fine pitch and a large diameter will have a small lead angle, whereas a screw with a coarse pitch and a small diameter will have a large lead angle.
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.
Formula symbols:
- n – Number of starts
- P – Pitch of the thread (Inch / mm)
- d2 –Pitch Diameter of the thread (Inch / mm)
