For thread repair tool set. Perfect for repairing threads in cylinder head or cylinder block. This is not the brand helical coil, but a massive twisted steel bushing. The advantage is that you can glue it perfectly with Loctite, the cannot get inside. Very easy to mount. After reparation as strong as original. After reparation with this set, you can easily tighten and turn repeatedly the bolt in the timesert without damaging the thread.