Page 8 - Threading_Handbook

INTRODUCTION Lead Lead Single-Start Pitch Double-Start Pitch Triple-Start
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.

Lead
Lead
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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