"John Manders" wrote in message
...

"Alan Horowitz" wrote in message
om...
I've got an old screw pitch gauge that I inherited. There's no mfr's
name marked on it, just "Number 137".

the individual leaves are marked with two numbers each, but these
numbers are not reciprocals. The first number is always a small
integer which I presume is threads-per-inch.

the second number is always a decimal.

All the leaves are of equal thickness, so they are not thickness
calibrations as in a feeler gauge.

Any idea what the second set of numbers are?

Depends upon whether it's metric or imperial.
The most likely is that the first is TPI, as you say. The second is
probably
the bolt diameter in a thread series. The most likely is BSW.

John

The second set of numbers, decimals, is the double depth of the thread pitch
..

Harold