Jumping in late but just so you know...
Plumbers are odd folks compared to carpenters. A carpenter wants to know how big a hole to drill for the pipe to fit through. The plumber measures the inside diameter to know how much water he can get to flow through it.
I've had many a weekend warrior insist the 1/2" pipe he has in his hand is really 3/4" and he is right as far as the size hole he needs to drill in the joist but not as far as what should be on the label of the fittings he needs. Let's face it, all the labels in my and every other store can not be wrong so the way you look at it needs to be adjusted.