Robinson's Aluminum Pro pinions feature lightweight aluminum construction withan added hard coating that produces extra strenght and less friction. Thesepinions also feature a hollowed out core that reduces rotating mass for improv-ed acceleration and deceleration. Available in 48 pitch from 12 to 35 toothsizes, and in 64 pitch in 16 to 47 tooth sizes.INCLUDES: 1 64pitch pinion 39 teeth 1 4-40 set screwREQUIRES: 0.050 size hex wrench such as GPMR8000.