Screw Jack - Effort Force vs. Load

A screw jack is a mechanical device that can increase the magnitude of an effort force.

Formula

The effort force for a screw jack when neglecting friction:

F = (Q × p) / (2π × R)

where:

• F = effort force at the end of the arm or handle (lb, N)
• Q = weight or load (lb, N)
• p = pitch - distance or lead of thread in one turn (in, m)
• R = lever-arm radius (in, m)

The torque acting on the screw:

T = F × R

where:

• T = torque (lb in, Nm)