I am trying to convert a 6-speed Dura Ace 7200 cassette hub to single speed. Bought a conversion kit and all fits except the retaining ring (A). Note that the inner diameter of the retaining cassette gear (B) is larger than (A). QUESTION: can anyone point me to any kind of threaded nut in lieu of part A? Please don’t suggest simply screwing on part B or somehow shaving the gear teeth of part B, as I don’t view those as adequately elegant solutions.