well, they aren't wave washers either. They are just shims. SunTour seemed fond of them for some reason. They take up a small amount of space, and maybe(??) provide some protection from wear for the aluminum.

In their freewheels, it seems like they select how many shims to use individually in order to get the desired clearance in the bearings. With the derailleurs, some days I think they did the same, but that's just casual observation and not a detailed review of a number of them. It does make me worry about used derailleurs that might be missing a shim. Hasn't been a problem yet, though!

Steve in Peoria