I need to replace a water shut-off valve below my kitchen sink. I see
that valves come made to fit on either 1/2" or 5/8" pipe. When I
measure the copper intake pipe with my (not very accurate) caliper it
measures .66, which is a little over 5/8". I think I read somewhere
that "1/2 inch" refers to the inside diameter, and that the outside
diameter is closer to 5/8. True? No?

So, what do I have, 1/2" or 5/8" copper pipe? I'm thinking 1/2" because
it's more common, and if it were 5/8" the outside diameter might be
greater than .66".

Also, Home Depot has valves with Shark Bite connectors which don't
require compression fittings. Are those things reliable?