From what I understand, the torque ratings on different parts are based on the amount of clamping force that the part in question can take. Using that measurement, engineers calculate an appropriate torque for the fastener that is affecting that clamping force.  However, when torquing your parts it's a good idea to aim a little low and then increase torque if nessisary to keep the part from slipping. If you are given a torque range, I usually use the low end of the range and move up as needed. If pink is the new black, 3 nM is the new 5nM.