Sandvik Coromant Threading - Manual (Page 31)

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2. Applications – Thread turning
Multi-start threads
Threads with two or more parallel thread grooves require two or
more starts. The lead of this type of thread will then be twice that
of a single-start screw.
The lead increases relative to the pitch by a multiple equal to the
number of starts. On a single-start thread, the lead and the pitch
are equal; on a double start- the lead is twice the pitch, on a triple
start- the lead is three times the pitch etc.
To produce a multi-start thread, make a single thread groove with
a number of passes, followed by the second thread groove with a
number of passes, then the third thread groove with a number of
passes.
Third threading groove
First threading groove
Second threading groove
Lead
Lead Pitch
A multi-start thread
with 3 starts