Posted by Robert Suijlen on 01/03/2023 12:57:06:
Hello Bill, saw the first two above allready, allthough the "double start" or "2 start" as the ad says I do not understand what it means!
If you are measuring the pitch as 12 tpi, a double start thread that measures thus is, roughly-speaking, two 6 tpi threads parallel to each other.
You can do a quick check to confirm or deny it: Poke a scriber point into the vee of the thread and rotate the cutter 360 degrees. See how far the scriber point advances. If it is 1/12", the thread is single start. If it advances 1/6", the thread is double start.
Post number 8 here suggest multi-start also:
https://www.homemadetools.net/forum/large-slot-drill-sidelock-chuck-lathe-66573