... -locking Trapezoidal Screw,etc;3. Safely self locking, Positioning Precision, Heavy Duty, Uniform Lifting Speed, Low Efficiency, Use Infrequently, Easy Installation, Low ... ,Lowering,Pulling,Pressing,Pushing,Rolling.5.Availabity: Manual Operation and Electrical Operation are available;6.Multiple Screw Jack Systems are availbale ...