This chapter reviews the assembly process and explores why the control of that all-important clamping force on the joint is so difficult. If pure torque control had been used, as originally planned, the results obtained would have been drastically different. The bolts with rolled threads achieved a higher average preload for a given torque, and the bolt-to-bolt preloads were less scattered than the bolts with cut threads. The length of time between calibrations depends on things as the importance of the joint being tightened, the environment in which the tools are being used, and the stability of the tools. The coefficient of friction is very difficult to control and virtually impossible to predict. Many investigators have found that nut factors determined on a sample or prototype joint, in a laboratory, can often differ significantly from nut factors determined on the actual joint in the field or on a production line.