Progressive Suspension PS-990-1001 990 Sport Series 12.5" Rear Shock Absorbers Black w/Piggyback Reservoir for Dyna 91-17The most adjustable shock in the V Twin market, the 990 Sport series shock features complete adjustability with a 0. 4 adjustable height eyelet, rebound damping adjustment, High & Low Speed compression damping adjustment via easily accessible knobs, and threaded hand adjustable spring preload. The 990 features a high pressure monotube with deflective disc damping routed through two unique circuits delivering a consistent feel through the damper stroke