Stripped Bolt and Screw Repair

Ever try to tighten up a bolt and it just won't? Or maybe you are putting the final torque on one and suddenly it gives way to being loose again. Whatever the situation, it is almost always accompanied by a sinking feeling in your stomach. Now what do you do?


Many times it is an easy repair, and almost any situation can be fixed with some sort of threaded insert. This term refers to exactly what it sounds like. It has threads on the inside that match whatever size of bolt hole you are trying to repair. The outside is also threaded, but of course a larger size. Usually, the offending bolt hole is drilled out on a drill press, and re-tapped to match the outside threads of the threaded insert. Then the insert is screwed into the hole, and you are ready for action again.

Steel Thread Insert
The most common threaded insert is called a "Heli-Coil", but this is a brand name. The industry name for this item is a Steel Thread Insert, or STI. It looks very much like a compressed spring. The coils of the spring form the inside and outside threads for the insert. If you were to cut the wire of this little spring, however, you would see that instead of round wire, a 60-degree diamond shape is used. This shape matches the common shape of most threads.


These are not the strongest inserts available. If you are repairing a high-torque bolt hole in a weaker metal such as aluminum or magnesium, then some other sort of solid, rather than spring-like insert, should be used.


These STIs are very small, so if space is an issue then they're a good choice. They are relatively easy to install, and the installation kits won't break the bank. STIs are a very good idea in difficult to reach spots, or in softer metals that may require repeated installation and removal of the actual bolt.