Worm Gear Screw Jacks with full name Worm Gear Machine Screw Jacks. 10 kN to 1000 kN Capacity. Machine Screw Jacks vs. Ball Screw Jacks are good choices for reliably lifting and positioning loads. If slower movement, low to moderate duty cycles and self-locking are required. Trapezoidal Machine Screw Jacks will be choosed by professional designers and engineers.