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Design and Theory

The difference between lead and pitch
In ball and lead screws there are often multiple threads, or multiple starts, running up the screw.   These are referred to as multi-start screws.  If the screw is a multi-start screw the lead and pitch are not the same.

Lead is the distance the nut travels with one revolution of the screw.
Pitch is the distance between two lands on the screw thread

For single start screw, the lead = pitch.
For double start, the lead = 2 times the pitch.
For four start, the lead = 4 times the pitch.

In the following animation the screws are all turned one revolution.  These screws all have the same pitch but different leads.  The arrow moves along the screw as a ball nut would move when the screws are turned.  Notice how the double start moves the arrow twice the distance of the single start.  And the four start travels four times the distance of the single start.

Lead vs. Pitch animation

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