Abstract: An improved throw-away, or single use, adaptor particularly useful with depressed center grinding wheels is described. The adaptor comprises a hollow mandrel having an internal threaded portion for attaching the adaptor to the shaft of a grinding machine. The hollow mandrel has a saucer-shaped disc portion extending axially from the outer portion of the mandrel. The saucer-shaped disc portion has a concave surface and a convex surface. The concave portion is equipped with a plurality of internal rib members and has a flange around the periphery thereof to contact the side of a grinding wheel. The flange portion has a plurality of protrusions, or bosses, thereon adapted to be received in corresponding orifices in the grinding wheel. In operation, as the grinding wheel contacts a work piece, the torque, or stress, is directly imparted to the adaptor, as the adaptor is threadably attached to the shaft of the grinding wheel.