J. Clarke wrote:
Got the bright idea of using a 1/2" copper pipe union as a bushing and
then realized that I don't have a drill bit the right size. Looks like
it's a tight 11/16, an 18mm, or a slightly loose 23/32. Anybody know
offhand which one is right?

If you epoxy it in, use the 23/32 or 3/4". If you are press fitting it,
use the 11/16. If the press is too tight, perhaps freezing the coupling
to shrink it a bit first would help.

Out of curiosity, what are you using it for? I use them for file and
chisel handles I turn, they look really nice all shined up and
varnished, even after 30 years of hard use:

http://jbstein.com/Flick/Handle.jpg
http://jbstein.com/Flick/Handle2.jpg

Also, I measured an old 1/2 fitting with my new 6" HF digital caliper
and also got 23/32. The caliber is on sale 7/2 to 7/5 at HF fo $15. I
of course paid list on an impulse buy.
--
Jack
The Problem with Socialism is you eventually run out of Other Peoples Money!
http://jbstein.com