In my experience, --> types 57, 63, and 93 (plus some later ones) all use the same 122 mm BCD bolt circle. --> 63 and 93 use 10 mm. bolt sets for coupling the rings to the spider, 57 uses smaller diameter bolts. --> 57 and 63 have crank profiles like 49d; 93 is much stouter.
hope this helps. Heck, hope it is right! harvey sachs mcLean va (I've only owned one type 57 chainring).
Jerry Moos wrote: I guess I learn something every day. I thought the model 49D had 10 mm holes to attach the inner ring, and that the 10 mm bolts carried over to mods 57, 63 and 93. But evidently not. Can anyone confirm that early mod 49s had 7 mm bolts for the inner ring? I always wondered how, if at all, mod 57 and 63 rings were different from mod 93. It seems the mod 57 at least had smaller holes. What about mod 63?