I have several lenses missing their flanges. I have thread guages and callipers so I can measure the outside diameter of the threads and the threads per inch and check the thread angle. But many are significantly worn so the outside diameter of the thread is not as large as it once was. Has anybody got any suggestions as to how to adjust for or take into account this wear? I would like to specify to the machinist what I need as getting lenses there and back is fraught with potential problems.