How would you connect a 1/2" copper pipe to a 1/2" galvanized iron pipe that has been cut and has no threads? Do I need to re-thread the iron pipe, screw on a brass attachement and solder the other end to the copper? If so, what is the name of the tool use to re-thread the iron?

You are right on track about threading the galvanized (see pic. Below). They rent threaders at all tool rental stores... you need a 1/2" ratchet die. They will probably only rent the whole kit. You will also need to rent a wrench to hold asgainst yourself when cutting the threads. Also, buy some cutting oil...

If possible, you may be better off removing the galvanized pipe BACK to the nearest coupling, elbow, tee, etc., and then installing new copper male adapter...

Let me know what you think..? Mark

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I'd go with Mark's suggestion about removing the pipe back to the next connection. Cheaper, easier, smarter.