Abstract: An adjustable V-belt pulley which may be selectively changed form one predetermined effective diameter to another without tools. The pulley comprises first and second separable pulley halves having juxtaposed frusto-conical faces adapted to receive a V-belt pulley therebetween. A plurality of spaced lugs extend axially from the first pulley half and a plurality of sets of cavities are provided in the second pulley half, each set being adapted to receive the lugs of the first pulley half. Each cavity set has a different cavity depth so that the effective pulley diameter is established by the choice of the cavity set into which the lugs are inserted. The pulley halves are concentrically disposed on a shaft and are held together by a wing nut or knurled nut on the threaded shaft end which clamps the pulley halves against a shoulder of the shaft.