Only thing I would add on this -- from recent experience -- is to be careful how you measure. If you try measuring from the outside the plates (rivet-to-rivet), you may get the wrong result (specifically, showing less wear than there actually is). You really need to measure inside (roller-to-roller). As such, one of the tools available for this is not a bad investment (Park CC-2 or CC-3). Either one is cheaper than a new cassette . . .