Advantage:Our roller trolley assembly is made of iron material, high hardness, smooth surface treatment, no burrs, strong and durable.Designed with three screw holes in 1/4 inch thick steel plate, we suggest you use M5 bolts. To Install ceiling trolley system or electric lift at will, easy to operate.Our silent electric hoist trolley uses deep groove ball bearings to ensure that you can operate it smoothly without making too much noise, providing high stability.4 wheel trolley assembly for secure use in many occasions, electric lift, ceiling mounted pulley system, cantilever rolling door, hanging boxing sandbag,etc.Specification:Material: ironColor: Silver ToneSize: 8 cm x 3.4 cm x 4.5 cm/3.15 inch x 1.33 inch x 1.77 inch(L*W*H)Package Included: 4pcs x 4 wheel trolley assembly .