Barrel bushings with Riot plugs combined made for Aera K4 trucks.
Bushings - They start as rods of our perfectly cured, high-quality blend of urethane we call RiotThane. They are then turned on a lathe and profiled to very a precise outer diameter. We then machine the hole in the bushing, keeping our tight tolerances, to ensure that the bushing fits SNUG on the kingpin and is perfectly concentric with the outer diameter. Lastly, we part the bushings off to tolerances often not seen in molded bushings. This ensures very precise alignment of the hanger on the baseplate. With the bushings being machined, we can guarantee a near perfect product every time.
RiotPlugs - RiotPlugs mimic spherical bearings in that they reduce translation of your hanger through a turn, thus letting the hanger pivot around the kingpin correctly. This gives much more accurate and responsive control over your steering input and output.
Why combine them? When combined, the plugs stays in place better and lasts quite a bit longer than normal.
Sold as a set of two.