I am installing compression valves and wall flanges on 1/2" copper (for sink & toilet supply). For some reason I am having trouble making sense the sizes available. I bought a flange for 1/2 copper and it is too small. Not sure if I bought the right thing.... is 1/2 nominal copper correct? I'm confused...
1/2" is a standard size. There are two type of 1/2" copper Type M and type L. I have allways gotte them mixed up the difference is in the wall thickness. Also the thicker one (I think is the type L) is harder to fit compression fittings and all 1/2" fittings for that matter. But they will fit if no burs are present. If the compression ring is really to small you must have the wrong size.
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Plumbing pipes are measured by ID (inside diameter) which means 1/2" copper is actually 5/8" OD(outside diameter). This is why your'e flange did not fit, you need 5/8" escutcheon and 5/8" compression valves.
As far as the difference between the types of copper L,M,K, the OD is not effected by the extra thickness only the ID. M is thin wall and L is thick wall and most common for potable water piping and type K is usually soft roll which is the thickest.