markings on Screw Pitch Gauge?

In article 1e3670a7.0402091459.5206f388
@posting.google.com, says...
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?


Probably the depth of the thread--handy to know if you're
cutting threads on a lathe. If you post a few examples it
would be easy to verify this.

Ned Simmons