Progressive 412/413/512 series shocks are the first aftermarket shock designed specifically for ATVs. They have undergone extensive R & D to provide the finest possible shock for your ATV. Progressive ATV shocks come with springs installed. Front shocks and some Rears are sold in pairs. 412/413 Series Features: Progressive rate springs for a comfortable ride and improved load stability All steel double wall damper with multi-stage velocity sensitive damping Five position cam style preload adjuster 512 Series Features: Progressive rate springs for a comfortable ride and improved load stability Five position pre-load adjustments Velocity sensitive damping for a smoother ride Gas charged damping consistency Equipped with “Shock Sox” to help keep springs and adjusters clean