45 degree shower elbows are generally 1/2" npt pipe (that measures .84" o.d.) so the pipe that is stubbed out should be a 1/2" galvanized nipple (.84" o.d.) with a cap. That way whoever the plumber is, he can simply unscrew the nipple from the female drop ear 90 fitting that was roughed in and screw the new 1/2" shower head 45 elbow into the drop ear fitting.