I don't think some of you guys really know how the thread chasing dial
works , so here are the rules of the thread chasing dial.....

_thread (lead) to cut_ on an Inch leadscrew (eg 4TPI)

multiple of the lead screw (on a 4tpi machine cutting 4,8,12,16,20 etc)
you can engage the dial anywhere it fully engages

Even number of threads can be engaged on any division (1, 1-1/2, 2,
2-1/2, 3, 3-1/2, 4, 4-1/2) remember not the quarter divisions that are
not labeled

Odd number of threads can be engaged on any main division (1, 2, 3, or
4)

fractional half pitches like 1-1/2, 6-1/2, 10-1/2 etc, can only be
engaged on opposite divisions (1 & 3) or (2 & 4) or (1-1/2 & 3-1/2)

Fractional threads that are not half pitches like 2-3/4, 11-1/4 etc can
only be engaged on one division, once you pick a division, you must
stick with it.

Metric, Diametrial pitch, Module pitch, and Inch Pitch, once engaged
cannot be disengaged, you will have to reverse the lathe and backout
the tool *do not disengage*

some exceptions to these rules are thread chasing dials with divisions
that are not 24 divisions (some TOS lathes have 16 divisions)

It's not rocket science, and this does work.

-S