Super hard, heat treated, “Absolute” pinion gears are a must for using with steel spur gears and will last and last if used with plastic spur gears. In sizes 9 through 23 teeth. All pinions stamped with tooth number. 1/8 inch bore. One 5-40 set screw included. 1/16 inch allen wrench (NOT INCLUDED) fits the 5/40 set screw.