... Heavy Duty, Uniform Lifting Speed, Low Efficiency, Use Infrequentl screw jack lift Configuration: Worm Gear, Worm Shaft, Taper Roll ... Bearings, Seals, Housing, Self-locking Trapezoidal Screw,etc.* Model: RN-0.5ton, RN-1 ton, RN ... Rolling.* Manual Operation and Electrical Operation are available.* Multiple Screw Jack Systems are availbale and fully synchronized.* Absolutely irreversible ...