Clamp down to stop and prevent unplanned movement of trailers from dock and storage areas. Deter unauthorized drive-off of trailers by blocking access to emergency brake airline. Attach Glad Hand Lockout to the trailer's (red) line connection, and secure with choice of padlock (sold separately) to control access. Visible red, octagon-shaped device is made of durable plastic with zinc-coated steel pin for hinge. Measures: 4" L x 3" W x 2" H.