This is the Upright Set for many HPI RS4 Cars. Includes right and left side Black plastic construction One left front hub and knuckle arm One right front hub and knuckle arm The hub is the part that attaches to the outside of the front suspension arms. The knuckle arm goes inside the hub, and the front bearings go in it to support the front axle. These parts are also part of the steering mechanism. This part is stock in the following vehicles: RS4 Rally, RS4 Pro, RS4 Sport, RS4 Mini, RS4 Mini Pro, RS4 MT, Nitro RS4, Nitro RS4 Racer, Nitro RS4 Mini, Nitro RS4 MT snew 06/27/00 ir/jl &