430 series - Better. High pressure nitrogen charged with deflective disc damping. Threaded preload adjuster will allow adjustment without tools. Chromed steel body with machined aluminum spring covers. These shocks can be mounted upside down if desired. With chrome covers and chrome springs or black covers with black springs.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.