Review on 1221-308 Thread Repair Kit - Enhance Your Thread Repair with Thread Kits by Adam Hardy

Excellent product. I've used them to fix tight threads on 3 different used gearboxes (all aluminum cases). I was able to successfully repair a small thread (m8) to a larger engine mount thread (M14). They are very durable but you have to be careful when installing them. The inserts are tightly coiled springs. So if you try to push them in you risk breaking the winding and ruining the insert. Regardless, my most recent repair took less than 10 minutes from start to finish.