Progressive's 444 Series Shocks feature a proprietary patented Frequency Sensing Technology (FST) that has the unique ability to dynamically adjust damping as you ride. FST allows the shocks to sense the frequency of a bump and automatically adjust damping for superior ride quality. A top mount threaded preload adjuster allows for fine-tuning with a simple twist of the cap. Deflective disc valving Adjust spring pre-load by hand, no special tools needed Progressive rate spring Available in Standard Duty, Heavy Duty, and Super Duty Black or Chrome finish Lifetime Warranty