Originally Posted by
juvela
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you show the threads on the cup but what about those in the shell?
you could test fit another metric thread fixed cup as a diagnostic
if shell threads slightly damaged you can make a chasing tap by cutting slots into an old metric fixed cup with a bench grinder/die grinder/Dremel tool
such a chaser is not capable of making new threads but can reform damaged ones
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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.