Backside wheel axle for big ball-bearings constructed from world-renowned HUDY Spring Steel™. Strategically machined for toughness and light-weight without compromising power. The wheel axle is likewise hand ground for optimum precision to be certain an excellent, accurate easily match suspension system ball-bearings, guaranteeing perfect wobble-free fit and rotation. Heat addressed for maximum power, durability, minimal use, and extra-long lifespan. Fits just multi-adjustable straight back upright #323355.