No, I was referring to copper fittings and pipe, the kind that you solder together.
I was just at the hardware store, and I had my tape measure with me!
I also measured a threaded PVC 90 elbow (schedule 80), and the inside is still 3/4", and in the same bad mitre configuration. In other words, to get that sweep in an elbow, you really have to use the copper fittings.
3/8" fittings are good for 1/2" tubing, but the actual curve in the fitting is narrower than the connection, probably more like 3/8" (go figure!).
I asked my buddy Roger what cheap pipe bender he used: I'm going to have to try something myself.
Now if only there was 5/8" copper parts available anywhere, then I might be able to clamp my 3/4 tubing to it. (btw, the 3/4" fitting have an OD of ~1 inch
).