These blocks have a rubber doughnut in the center to even out the wobbliness caused by the uneven floor pads. However the one which has no rubber under the clutch plate can be equally as good. On the bottom of the block are the usual hooks to hold the pad in place. It was designed for the 175 t0 300 rpm machines. You may use it on all Centaur floor machines or other make of floor machines. The clutch plate is universal for North American made machines.