Lead is the axial advance of a helix gear tooth during one complete turn (360°), that is, the Lead is the axial travel (length along the axle) for one single complete helical revolution about the pitch diameter of the gear.
Lead angle is 90° to the helix angle between the helical tooth face and an equivalent spur tooth face. For the same lead, the lead angle is larger for smaller gear diameters. It is understood to be measured at the standard pitch diameter unless otherwise specified.
A spur gear tooth has a lead angle of 90°, and a helix angle of 0°.
See: Helix angle
Read more about this topic: List Of Gear Nomenclature
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