A 29° trapezoidal thread form used for power transmission rather than fastening.
ACME threads are designed to move loads, not to clamp parts. The 29° included angle is shallower than a 60° fastening thread, which puts more material at the root and lets the thread carry heavy axial thrust — the reason it appears on lead screws, vises and valve stems.
The flat crest also wears better than a sharp V under repeated motion, and the thread can be split with an anti-backlash nut. A 60° thread used as a lead screw wears rapidly and loses accuracy.
Using a standard 60° thread as a lead screw. It will work briefly and then wear out of tolerance.
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