On 06 Jun 2021, Ed Pawlowski wrote in
alt.home.repair:

On 6/6/2021 8:47 PM, Nil wrote:
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?

You have 1/2" copper
1/2 OD 0.625 ID 0.545

Sharkbite fittings work well.

Thank you! I was going to buy two valves and return one, but I think
you're right.

The Sharkbite version will save me some work and uncertainty. I'm not
good with those compression ring fittings.