Which description correctly defines a screw jack?

• A. A hydraulic jack that uses fluid pressure to lift loads.
• B. A long, nonhydraulic jack that can be extended or retracted by turning a collar on a threaded shaft.
• C. A lever operated scissor jack used for small loads.
• D. A pneumatic jack that uses air pressure to extend.

Answer: (B)

A screw jack uses a threaded shaft and a nut mechanism to convert rotational motion into linear lifting. When you turn the collar, the nut travels along the threaded shaft, raising or lowering the load with high mechanical advantage. It’s typically a long, nonhydraulic device that relies on the screw thread rather than fluid or air pressure. In contrast, hydraulic and pneumatic jacks lift by fluid or air pressure, and a lever-operated scissor jack provides lifting through a scissor mechanism, not a screw. So the description that fits a screw jack is a long, nonhydraulic jack extended or retracted by turning a collar on a threaded shaft.