This is the best yet Printrbot Large and Small Gear set. Beautiful, precise, and ready for use on your jr, LC, or Plus. They are molded in black Nylon with extremely high tolerances. Absolutely smooth as butter. The small gear requires a flat on part of the motor shaft, but they are common and we sell them if you need one. You will never buy another large and small gear. When properly installed, backlash is imperceptible. Sexy and no slop.