wrote in message
...
I did take a sample to ACE Hardware this afternoon, they measured and said
was about 1/16 inch larger than 1/2 inch copper......I do not believe it
is
5/8....I just checked and compared with some new 1/2 inch I had in
basement
and there is just slight difference in size.... pretty much, they look the
same to me.

That would be 11/16 then. Or very close to 17mm.
Get a micrometer and get the actual size and you may do better finding what
you really need.

Try these guys
http://www.worldwidemetric.com/fittings_coper_sol.asp

I have no idea why metric tubing would be in a US house built that year
though. It would not be common at all.