This 16k UFP A-160 (16,000# Capacity) Hydraulic Disc Brake Actuator is for tandem and triple axle disc brake trailers. This actuator has a back-up solenoid that works in conjunction with the reverse light wire of the tow vehicle. While tow vehicle is in reverse, the solenoid is energized which does not allow fluid to the brake calipers, which allows the trailer to be backed-up. Some tow vehicles may need to be wired for this to operate as designed. The coupler requires a 2-5/16” (min. capacity 16,000#) tow ball of the correct rating. Not included.