worm screw lift; Safely self locking, Positioning Precision, Heavy Duty, Uniform Lifting Speed, Low Efficiency, Use ... liftConfiguration: Worm Gear, Worm Shaft, Taper Roll Bearings, Seals, Housing, Self-locking Trapezoidal Screw,etc.* Model: RN-0.5ton, RN-1 ton ... , RN-40 ton, RN-50 ton, RN-100 ton.* Safely self locking, Positioning Precision, Heavy Duty, Uniform Lifting Speed, Low Efficiency, Use ...