Originally Posted by Road Fan

Another too that can help is a thread restoring file, from McMaster-Carr. It has a set of teeth you can run along the damaged threads. It won't restore steel which has already been lost, but it will help to cut the remnants of the old threads to that threading can happen between the cup and the BB inner surface. The strength will not be exactly what it was because the threads have lost some material, but it will often result in usable parts recovered from an absolute disaster.for a french 10 threads per centimeter thread, the too has a 0.100 edge.