444 series shocks: Comes with FST (Frequency Sensing Technology) which dynamically adjusts damping; according to road surface. Top mount threaded hand adjustable preload. Note: Optionally available is 704545 for an optional QPS (Quick Preload System) adjustment kit. It replaces the stock upper shock caps of all 444 & 944 series Touring shocks; allowing quick preload adjustment without removing the saddlebags. What are Progressive Suspension''s ''Heavy Duty'' shocks? If you are a lightweight rider with a lightweight passenger; STD Duty is probably your best choice; heavy duty shocks will give you a harsh ride. For Big Guys & Gals with a lot of baggage; Heavy Duty springs are the way to go. Heavy Duty is not better; it''s different.Heavy Duty shocks or springs are recommended to be used on motorcycles that are operated at or near the manufacturers maximum load rating over 50% of the time. In short: Standard is good for combined rider weights up to 250 lbs / 113kg); Heavy-Duty (250 lbs / 113kg to 350 lbs / 159kg) and Super Duty (350 lbs /159kg and up).