The Double Deep Top-Track system combines two Top-Track systems into one larger track shelving system. Connected side by-side shelving units, up to 10.5 ft. (3.2 m) long, roll along the overhead tracks. Includes four 74" (1880mm) high mobile posts, four casters, donut bumpers, guide rollers, and other hardware to assemble a mobile unit. Shelves are sold separately. Each double deep mobile kit includes 8 posts.