These trollies are dependable, easy, and safe to use. Designed to easily adjust to the width of virtually any S, H, W, and M type I-beam. Width is adjusted with manual screw mechanism. Includes locking ring to prevent trolley width from changing accidentally. Manual screw mechanism may also be tightened to prevent trolley from moving (similar to a Beam Clamp). Each trolley includes four rollers with sealed bearings for long life. A lifting eye is located at the bottom of the trolley for attaching a hoist (sold separately). Steel construction and painted finish.