Lead: the axial distance between two corresponding points on a helix. When a threaded part is rotated about its axis with respect to a fixed mating thread, the lead is the axial distance moved by the part in relation to the amount of angular rotation. On a double lead thread (double start), the lead is equal to twice the pitch. It is necessary to distinguish measurement of lead from measurement of pitch, as uniformity of pitch does not assure uniformity of lead.
Original Posting: 3/20/2012
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