What he said...
It does look like 1/2" copper and it does look soldered...
This sounds like it's a temporary thing, so another approach is to affix a 1/2" threaded fitting on the end of pipe...and buy a piece or pieces to convert that to a hose fitting...and when done, just screw on another 3/8" valve like you have to it. Use a few wraps of teflon tape.
In NJ--Tierney's in Montclair, Sept. 25, 7:30 p.m.
In NYC Sat, Sept. 30, 8 p.m. at Broadway Comedy Club! Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Comedy can be a great cheap date!
Mangofy your E46!