... and low frequency. Precision trapezoid screw pair and high precision worm-gears pair. screw jack: worm screw lift, screw lift, worm lift:Economical: Compact ... load, low speed, low service frequency.Self-lock: Trapezoid screw has self-lock function, it can hold up load without ... braking device when screw stops traveling. Braking device equipped for self-lock will ...