For traliers equipped with disc brakes. This model come with the  reverse lockout solonoid installed. The model 66 capacity actuator provides greater towing capacity (6,600 lbs.) than traditional 6,000 lb. capacity actuators. The patented all aluminum master cylinder incorporates the shock absorber into the master cylinder assembly. This exclusive product feature was designed into the master cylinder in order to provide th tow vehicle operator with an early warning signal when the brake fluid is at a low level. Tie Down's oversized master cylinder provides the pressures required to run disc brakes and the added brake fluid volume to run multi-axle configurations. Other features of Tie Down actuators: thicker gauge coupler hitch, quick bleed access design, pre-drilled and tapped for reverse lock out soloniod,  vinyl coated tension coiled safety cable and stainless steel ball latch safety pin. Ball size: 2", Frame width: 3".