i use hot bodies spider gears in my strr diff cups without an issue. they are stronger and the almost the same weight as the kyoshos. i have used aftermarket jammin machined aluminum diff cups as well, works great but if you forget to threadlock the bolts, they will back out of the ring gear and make a mess. from what i have seen kyosho, jammin, and hot bodies use the same internals, just different materials. hot bodies out drives seem to wear out faster than the kyoshos. kyosho strr ring and pinions will last as long as shimmed properly and new bulkheads are used.