HPI stock replacement pulley set for the Nitro RS4, Nitro Racer, Nitro Mini and the MT RS4. Constructed of black composite plastic. Excess material removed to reduce weight. This product includes one right half main diff pulley. One left half main differential pulley. Two right half small pulley (18 teeth). Two left half small pulley. Two 8x10 metal bushings (fit on the outside of the main diff pulley). Four M2x10mm screws (for holding the main diff halves together. This will not work on the RS4 Sport or the RS4 Pro. This will do one differential, if customer needs to do both front and rear they will need to purchase two of these.