Jacks are used to prevent up-ending semi-trailers when they are not connected to a tractor during loading and unloading operations. Also used to level trailers parked on sloped ground and to prevent k landing gear from sinking into a soft surface. High strength steel construction. Flush-type zerk fitting for lubricating ACME screw. Meets OSHA regulations when used with wheel chocks. Powder coat safety yellow finish. Includes reflective collar for visibility at night.