It is not unusual to find the fuel inlet threads on your 1957 to 1966 end carbs worn out. If you see Teflon Tape on the fittings, or if the brass fuel fitting screws all the way in and is not tight, you likely need this service. It requires you to send me the air horn. The new thread insert is not a Heli coil, but similar. The fuel inlet threads are tapered (1/8" NPT.) I have a special fixture that your air horn bolts onto. This fixture is secured to my drill press to make sure the new threads are aligned perfectly. The new insert is not visible when lines are installed. It is more of a barrel type insert than the Heli coil. I have never had a problem with them. Price includes insert and machine work , as well as a new air horn to float bowl gasket. Shipping charges of $10.50 is per air horn Priority mail. Inquire if out of the United States. Best to e-mail me about this service, as you will need my address and a timeline to get the parts back. I can usually do these in 2-3 days and get them out to you. Save an air horn!