Abstract: A rotatable disc comprising a plurality of generally parallel plates tightly joined together for rotation about a hub. Each plate is provided with a plurality of angularly spaced lands projecting from a face thereof, the lands of each plate interposed in alternating relationship between the lands of the next adjacent plate. In this manner, circumferential displacement of adjacent sectors in any one plate is prevented in the event that a crack develops therein. Each plate is redundantly sized such that, in event of structural failure of one plate, the remaining plates can support a proportionate share of the load of the failed plate. In one embodiment, the plates are prevented from separating laterally through the inclusion of generally radially extending splines which are inserted to interlock cooperating, circumferentially adjacent lands.