Summary

This plug seals up the hole in the side of the gearbox that allows access to the set screw and prevents oil from spilling out of the gearbox as well as keeping dirt out.

My senior design project used 9 of these gearboxes on a robot that traveled in sand. This bolt on plug kept the internals lubricated and clean so we didn't have to keep rebuilding them.

I used 10-32 x 3/8 bolts to mount them, though 10-32 x 1/4 should work as well.

Note: when oiling the gearbox, run them in clean conditions for a few minutes first to allow excess oil to drain out. If excess oil gets trapped inside, it will try to get into the motor.