You must have the robinson racing spur, this is awesome as the stock part is plastic and melts if too much friction is applied.
Im running this with the RR Gen 3 slipper system. This replaces my fried "plastic" bushing that came on the slash 4x4. This item is a must have if you are experiencing alot of slop in the spur gear assembly. This larger and stronger bushing fits nicely within the drivetrain bearing and keeps everything nice and tight, thus eliminating the slop I used to get from the plastic bushing. If you are experiencing constant spur gear burning....get this to eliminate it.