Leadscrew Torque to Lower a Load Formula

Equation for calculate leadscrew torque to lower a load is,

$$\mathrm{T_l}=\frac{\mathrm{F\; ·\; d_m}}{2}\times \frac{\mathrm{\pi \; ·\; \mu \; ·\; d_m-l}}{\mathrm{\pi \; ·\; d_m\; +\; \mu \; ·\; l}}$$

where,
F = Load on the screw
d_m = Mean diameter of the screw
μ = Coefficient of friction depending on the material
l = Lead
π = pi (3.141592653589793)
T_l = Torque