Based on our measurements (which match well with those posted above) and the part number, I believe it is the 16mm lead part listed in this table:
http://www.haydonkerk.com/LinearMoti...9/Default.aspx
That would put the efficiency at 80%, giving you all the values you need to calculate linear force from torque.
F = 2*pi*T*E/L
F = Linear force
T= Torque
E = Efficiency
L = Lead
You can do this calculation with any units, but be careful that your units all match. For example a lead in inches should be used with a torque in in-lbs to get a force in lbs.
The nut most resembles the BFW series with triangular flange:
http://www.haydonkerk.com/LinearMoti...4/Default.aspx
The table on that page puts the max dynamic load at 150 lbs for a 1/2" lead screw.