Progressive Suspension 412-4219C Chrome 12.5' Heavy Duty Low Buck Factory Replacement Rear Suspension Shock: Automotive. Buy Progressive Suspension 412-4219C Chrome 12.5" Heavy Duty Low Buck Factory Replacement Rear Suspension Shock: Shocks - ✓ FREE DELIVERY possible on eligible purchases. Durable design means they will be an improvement to your motorcycle's suspension performance . All steel double wall damper with multistage velocity sensitive damping . 5 Position cam style preload adjuster . High pressure gas charged for consistent damping performance . Heavy duty progressive rate spring . The 4s simple, durable design means they will be an improvement to your motorcycle's suspension performance for as long as you are riding it. The double-wall steel body construction with nitrogen charged, multi-staged velocity sensitive valve gives you smooth, consistent damping. A five position cam style preload adjuster lets you dial in your ride whether you're a light rider or heavy hitter. With multiple options like full show black covers or black springs in progressive rate and length 14. inch , there is sure to be a 4 that's right for you and your bike. Heavy duty progressive rate spring. . . .