PS, 444 series shock set. 13". Heavy Duty. Black 91-17 Dyna (Excl. 12-16 FLD Switchback)

444 series shocks - Best. 
Comes with FST (Frequency Sensing Technology) which dynamically adjusts damping, according to road surface. Top mount threaded hand adjustable preload. 

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.