How can I connect copper pipe to an unthreaded, galvanized pipe?
You have 3 or more options. #1 get a shark bite to go from galvanized to copper. #2 You need to go to a plumbing store and get a galvanized nipple and then extend your copper to the point the pipe screws into a coupling or other fitting. #3 If you don't want to extend your copper get an exact measurement and have a new piece of pipe cut and threaded. #1 is the easiest way and may be the most expensive but what you save in time is worth it. I may have used a Dresser compression fitting home depot calls them pattern fittings for galvanized repair in the wall I could not thread or remove but thought it was a shark bite.