Permanently attaches to face of dock, ready for instant use. Recommended for docks at least 45" high. Each unit provides a service range of 5" up, 5" down. When trailer departs, lip automatically drops behind bumper face. Concrete recess is not required. Comes with 2" x 8" x 18" bumpers. Simple operation. Place actuation handle into the hole in the inner lip, pull back toward the floor, then push forward up until leveler rests on truck bed. Hand pump and electric hydraulic operation also available.