Tool Time
The Best of Harley-Davidson for Lifelong Riders
Lets talk about fasteners and reasons for torque. When a fastener is tightened, an axial tension is applied to it. This stress stretches the fastener and reduces its diameter slightly. As we tighten the fastener more, we reach the yield point. Continuing to tighten the fastener moves it into the plastic range in which we are permanently stretching the fastener. If we continue to tighten the fastener, we will reach the ultimate tensile strength of the fastener and shortly thereafter the bolt will break. For any fastener to work properly, it must be stretched sufficiently to produce a static preload (clamping force) that is greater than the expected external loads. This is what the torque applied to the fastener does. Bolts and screws stretch like a spring and then return to their original length when tightened in the elastic range. It is critical that the fastener be tightened the right amount. Too little and they will loosen, too much and they may break or damage threads. Fasteners tightened into the plastic range will be permanently stretched and should be replaced.
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