I have a Rolleiflex bayonet filter and for the life of me, I can't figure out the size. It is bigger than Bay I, I am guessing it is Bay II, but I don't know for sure. There are no size markings on it at all. The outside diameter is just about 42mm, from what I can measure using my crude methods (metal tape measure and metric converter). Can someone tell me if this is a Bay II or III? I plan on selling the darned thing in the classifieds once I know what size it is. It is an 85 warming filter. Thanks!