Industrial trailer stabilizing jack, specifically a Vestil CJ-BEAM-PN
Vestil CJ-BEAM-PN is a heavy-duty, hand-cranked trailer stabilizing jack designed to prevent semi-trailers from upending or tipping during loading and unloading when disconnected from a tractor. It is a critical safety tool for any loading dock, designed to meet OSHA regulations when used in conjunction with wheel chocks

