PROFESSIONAL SPEED KIT ( 4 Machined Spacers + 8 Machined Speed Rings) Eight (8) x High-Precision steel 1.2mm thick Speed Rings and Four (4) x 10mm thick High Precision Bearing Spacers Treated with Black anti-corrosion treatment to prevent rusting Will never bend or compress like aluminum spacer sets Makes Bearings last longer and wheels slide smoother! Fits 8mm axles on longboards and skateboards