Pro-Line's Ultra Reservoir Shock Caps fit directly onto the stock X-MAXX shocks and transform them into fully functional reservoir shocks! The additional reservoir provides more oil volume to your X-MAXX shocks which results in cooler shock temps and improved shock consistency. The reservoir piston compensates for the volume of the shock shaft, delivering plush performance over small bumps and large jumps just like full-scale shocks! The included shock cap, reservoir, piston and bottom cap have all been expertly CNC machined out of high grade aluminum to exacting specifications to meet the demands of the enormous X-MAXX. The included o-rings provide the sealing you need and Delrin upper pivot balls are included for optimum performance.