If I use a copper tube with an inside diameter of .5in, outside diameter of 5/8in, what size fitting do I use?
Use the inside measurement.
If you are using 1/2 ID rigid copper piping, then when you ask for fittings or look for fittings you need 1/2 stuff. If you're sweating the connections you use 5/8 ID fittings, which will be called 1/2, because they refer to the ID of the pipe you're using, not necessarily the fitting. However, if you're using compression fittings then you need to ask for ID to fit the OD of the pipe, ie, 1/2 ID 5/8 OD., so you need 5/8 compression fitting. And it sounds like you're sweating a male pipe adapter fitting onto the 1/2 rigid copper, yes, it should fit right on the pipe. Just remember to clean, (sand or wire brush), both pieces, the male and female, and use plenty of flux on both as well. When you sweat, heat the fitting, not the pipe, when the fitting gets hot enough to melt the solder, it will flow right into the fitting.
If you are using 1/2 ID rigid copper piping, then when you ask for fittings or look for fittings you need 1/2 stuff. If you're sweating the connections you use 5/8 ID fittings, which will be called 1/2, because they refer to the ID of the pipe you're using, not necessarily the fitting. However, if you're using compression fittings then you need to ask for ID to fit the OD of the pipe, ie, 1/2 ID 5/8 OD., so you need 5/8 compression fitting. And it sounds like you're sweating a male pipe adapter fitting onto the 1/2 rigid copper, yes, it should fit right on the pipe. Just remember to clean, (sand or wire brush), both pieces, the male and female, and use plenty of flux on both as well. When you sweat, heat the fitting, not the pipe, when the fitting gets hot enough to melt the solder, it will flow right into the fitting.
Use the inside measurement.
