When load is applied to a bolted connection in the direction of the bolt axes, the residual clamping force on the joint is dependent upon the pretension of the bolt. Where bending action is also present, the fluctuating stress in the bolts may also be dependent upon the pretension. In most cases where an accurate pretension is required, the bolts are tightened by means of a torque spanner, and the pretension is then dependent upon the coefficient of friction between the screw threads of the nut and bolt. The effect of normally distributed variations in the coefficient of friction on the pretension is considered.
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