On Sun, 5 Feb 2006 16:57:40 +0000 (UTC), Frank Erskine
wrote:

I'm trying to find out whether the ¼" bush for a camera tripod is a
Whitworth or a UNC thread - both are 20 tpi, but of course the thread
form is different.

Officially Whitworth, but it really doesn't matter. You're only talking
about 5° difference on the thread flank and I doubt if many of these
threads are cut to that level of accuracy.

Leftpondian hardware dealers (I use Lee Valley) are full of 1/4 UNC
hardware, including screw-in bushes and tee nuts. These work fine for me
with camera hardware.