Thread restoration using wire thread insert (Heli-Coil)

If you have stripped a thread, you have several choices to rectify the situation and the two most used are:

1. Drill and tap to the next size up and use a larger bolt, or a stepped stud.

2. Fit a Wire Thread Insert.

There are several manufacturers of wire thread inserts including Heli-Coil. You can purchase the tools required as a kit or as individual items. The kit will include a tap of the suitable thread size, a thread inserting mandrel, a tang breaking punch and a quantity of wire inserts.

The process is relatively simple. As the thread has been stripped, the hole will have been enlarged, so it will probably not be necessary to enlarge the hole before commencing to tap the thread for the wire insert. The tap supplied in the kit will be a secondary or finishing tap with sufficient taper on the first 3 threads to start the threading process. Make sure that the tap is at right angles to the job. you are tapping into a blind hole that is shorter than the thread insert you may need a bottoming tap to create enough thread length to insert the wire.

Having tapped the thread put the wire thread insert on the mandrel and gently start to screw the wire thread into the threaded hole. Initially it will follow the tread in fairly easily but as you insert more of the wire insert it becomes more difficult to turn and you start to wind up the spring. It is at this stage it is possible to jump a thread if you are not careful. One way to help prevent this happening is to gently pull the mandrel outwards as you turn it; this keeps the spring coils together. Continue to screw in the wire insert until it has all gone into the threaded hole. Remove the mandrel and insert the tang breaking punch, a gentle tap should break off the tang and allow you to screw in a stud or bolt further than the end of the wire insert if required.