MST RMX 2.0 Aluminum Spool Set. This optional spool features an aluminum spool shaft, with separate outdrives that are held in place by cross pins – which are then secured in place by the bearings. This spool assembly is a direct replacement upgrade for the stock ball differential, and is a must have upgrade for brushless applications, or any application that can benefit from increased durability. Plus, the outdrives are double slotted to increase the useful life of the parts. Package includes spool shaft, outdrives, shims, cross pins, driveshaft blades and hardware.