Progressive Suspension PS-444-4002C 444 Series 13" Standard Spring Rate Rear Shock Absorbers Chrome for Touring 80-Up/Sportster 79-03/FXR 82-94Our 444 Series Shocks feature a proprietary patented Frequency Sensing Technology (FST) that has the unique ability to dynamically adjust damping as you ride; what this means is whether youre hitting the small or big bumps in the road, the shock distributes oil through ports accordingly to soak up the hit making for an ultimately comfortable ride. A top mount threaded preload adjuster allows for fine tuning with a simple twist of the cap. 444 Series