2. The Stage 4 system includes these massive upper and lower adjustable control arms. Each end twists independently and friction-free to allow big improvements in flex. Another cool feature is that each is greasable for long-lasting noise-free operation. A vulcanized rubber bushing isolates road vibrations at each end. Although they may appear to be similar to other control arms on the surface, what really distinguishes JKS arms are the features you can't see. For instance, ultrafine adjustment threads are far stronger than common coarse-thread designs. A slippery brass support bearing eliminates wear caused by leverage, and a spring-loaded seal keeps the lubricant contained and free of contamination. According to JKS, the end result is an extremely reliable design that outlasts anything else on the market.