Page 11 - Threading

Lead
Lead is the distance that defines an axial movement of any point moving in relative motion per one full
turn (360°) along a line parallel to the thread axis. In a single-start thread, the lead is equal to the thread
pitch. In a multi-start thread, the lead is equal to the thread pitch multiplied by the number of starts.

Single-Start Double-Start Triple-Start INTRODUCTION

Lead Lead Lead
Pitch Pitch Pitch

Lead=Pitch Lead=2xPitch Lead=3xPitch

Helix Angle
The helix angle of the thread influences thread efficiency and is necessary for calculating torque in
thread applications. The helix angle of the thread can be defined by unraveling the helix from the
thread, representing the section as a right triangle and calculating the angle that is formed.

φ= arctan ( P )
π×Dpitch

When:
φ = Helix angle

P = Thread pitch

Dpitch = Pitch diameter (effective diameter of thread)
π ≈ 3.142
φ
P φ 3
P φ 2 φ 1
πxD
πxD3
πxD2

πxD1

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