At 11:16 AM 11/27/04 -0800, you wrote:
>I ran across a thread that has puzzled me a bit. It's on a Cole's water
gauge.
>It appears to be a 7/32 - 32 thread. But the thread that I made doesn't
seem >to fit perfectly.
Royce,
Here is one possibility, depending upon the source of your taps and
dies. 7/32-32 is a standard (although uncommon) "Model Engineer" (aka ME)
thread. The ME threads are Imperial size 32 and 40 tpi threads developed
for use in model engineering projects (duh!) Although the industry is now
shifting to Metric, until recently most British model steam fittings had ME
threads.
However, the British 32 & 40 thread ME system is a 55° thread angle
rather than the U.S. standard 60°, and British ME threads also have
radiused crest and root as opposed to angled crest and root of U.S. threads.
The upshot of all this is that the two systems don't mix very well
and threads made with U.S.-made taps and dies will foul at the crests or
root with a British-made ME thread after 2 or so thread revolutions. The
solution is to run a tap or die (whichever is applicable) over the foreign
thread (whichever one you deem to be "foreign") and create clearance for
the crests & roots.
Then maybe not . . . . .
Regards,
Harry
