According to Robert Scibienski :
The indicator tables on lathes read, for various thread counts, a
single number, one OR another number, or either 1-4 or 1-8. How does
one interpret the dash indications?

Which brand and model of lathe are we talking about?

I think that the dash means any number between the two given,
with some lathes having numbers in the range 1 through 4, and others in
the range 1 through 8. (I've also seen some with the numbers only being
1 and 2.)

There is typically a '|' between the numbers, and for threads
which are an even multiple of the pitch of the leadscrew, you can close
the half-nuts on any one of those.

The "one or another" are typically numbers half-way around the
dial, e.g. for a 1-4 range, *only* even, or *only* odd.

IIRC, (without going down to verify it), my 12x24" Clausing has
1-4 as the numbers.

To be sure, with your particular lathe, set up for the threads
in question, set the tool depth to only put a fine scratch in the
surface (using the '1' number), and then try various combinations to see
which ones won't add a second scratch between the lines of the first
one.

Start with odd numbers (since you first used a '1'), then try
the even numbers, and if things are still fine, try any line, with or
without a number.

It helps to know what the pitch of your leadscrew is, so you can
tell which threads are an integer multiple of the leadscrew pitch.

Typically X-1/2 type threads will be only the same number.

Metric threads on an imperial leadscrew are "Forget about the
half nuts and the threading dial -- keep them engaged until your thread
is done", running the lathe backwards to get to the position for cutting
the next pass. Same with imperial threads on a metric leadscrew. (This
presumes that you have the necessary gears to set up for cross-system
threading.)

Enjoy,
DoN.
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