Originally Posted by
dsbrantjr
Since the lead-in threads are distorted or missing you may have difficulty getting a makeshift tap to start and run straight; gettting it started crooked or jamming it could cause more damage. Depending on the value of the frame involved, paying for the use of a proper tap could be a wise investment.
Good point! If the threads are more or less flattened out, you need to make sure that your makeshift chasing tool is on straight. The best way to do this is to thread it on by hand as far as possible. It's also highly unlikely you will be removing any metal, so there should be very little resistance. Best to use a short tool (ie 8") so you won't have enough torque to do any real damage.