Force generated by ball screw linear motor? Say I have a motor with a certain amount of torque, $T.$ It is turning a ball screw mechanism like this . 
Say, I mount something on the nut, I want to calculate the mass of an object I can lift upwards, i.e. the force that the actuator can generate.
I think this equation is what I want: $$T=\frac{Fl}{2\pi\nu}$$ source
But I don't understand:
$\bullet$ What is the "lead" $l\,?$ Is it the millimeter pitch distance between grooves? 
If so, using that tiny motor above (I have a similar one) it seems that $F = 2\cdot \pi \cdot 0.26~\mathrm{Nm / 8mm}$ which is $204$ Newtons, so equating to $F = mg$ it seems I could lift $204~\mathrm N/9.8~\mathrm{m/s^2} = 20.8~\mathrm{kg}\,?$  This seems really heavy for that small motor, so I figure something is wrong with my interpretations and/or calculations.
$\bullet$ How is the wikipedia formula derived? 
 A: lead is the pitch of the screw,it probably needs to be in meters if the rest of the equation is SI units.
Yes you can lift a very big load with a screw and a small force - that's why your car has a screw thread jack to change wheels.
Really a screw is just a slope (inclined plane in physics speak) so the equation should be pretty easy to derive.
edit: An easy way to check is to consider the energy. In fact whenever you aren't sure in a physics calculation ALWAYS consider the energy, it's often the simplest way.
One turn of the thread moves the object 8mm vertically.
If you have a Torque of 0.26Nm then one turn of the motor is like providing a force of 0.26N at a radius of 1m, and energy is force * distance.
So a force of 0.26N around a circle of 1m radius is 2*pi*1.0m*0.26N = 1.6J
The energy to lift 20kg vertically 8mm = 20kg * g * 0.008m = 1.6J 
A: I think this is far more a question for EngineeringSE, but just to hopefully clear up two points
 
The lead on a thread.
The derivation follows, but it's not exactly  the same as Wikipedia.

$\eta_{thread} \eta_{thrust}$  might be combined as efficiency in the Wikipedia equation.

If so, using that tiny motor above (I have a similar one) it seems that F = 2*pi * 0.26Nm / 8mm which is 204 Newtons, so equating to F = m*g it seems I could lift 204N/9.8m/s2 = 20.8 KG?? This seems really heavy for that small motor, so I figure something is wrong with my interpretations and/or calculations.

My apologies, I am an idiot, Martin's answer spells it out.
A: It is simple:
F = T*2*Pi*eff/l
Where:
F: Force, newtons; 
T: Torque, newton-meters;
l: lead, meters;
eff: ballscrew efficiency
In most cases, efficiency can be set safely to 90% with enough margin.
So, for example, a ball screw with 5mm lead, driven by 2Nm motor will give:
2*2*Pi*0.9/0.005 = 2262N = 231kg
