Original Posting: 3/20/2012 Last Revision: 10/19/2017 Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com

Multistart thread

Doublestart threadformula

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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 Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com

The following table chart are standard metric internal thread sizes M 9 - M 24 per. ANSI/ASME B1.13M-1995. These thread sizes and classes represent bolts and screws, as well, as other standard internal threads. Do not use these values for standard metric external thread design. All units in mm.

Single start threadchart

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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.

Single startand doublestart thread

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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.