Multiple start thread: a screw thread with two or more threads where the pitch is equal to the thread lead divided by the number of thread starts. Also called multiple lead thread.
Additional Discussion: Single-start threads are most common, and are more useful for general fastening needs. They offer more resistance to loosening than multi-start threads, due to the lower helix angle of the thread. Multi-start, aka: multiple-lead, is a thread that offers quick assembly and disassembly.
Thread lead can be described as the linear screw travel accomplished in one revolution. Thread pitch is the distance from any point on a screw thread to the corresponding point on the next thread, measured parallel to the axis. With a single-start thread, lead and pitch are equal. A double-start thread's lead is twice the pitch measurement.
Using 20 thread-per-inch thread as an example, the screw must turn 20 revolutions to advance 1” in the part. A 1/4-20 double-start thread has the same number of threads per inch, but with two starting points, 180° apart, needs just ten revolutions to advance 1”. A triple-start thread, with starts 120° apart, will advance 3 times faster than a single lead thread. The result continues to change appropriately as additional starts are added.
Original Posting: 3/20/2012
Last Revision: 10/19/2017
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