If we asked a handful of maintenance engineers what exactly they are trying to achieve when they tighten a bolt, it’s likely that we’d receive a wide range of answers. Strictly speaking, when we tighten bolts we’re trying to stretch the bolt enough so that the elastic tension within it clamps the assembly together. That’s right - it’s one that’s easier done than said! In a perfect world we would always recommend measuring the tension in the bolt, as opposed to the torque, because the tension is what we really need to know. In the real world, torque is the simplest way of achieving control in threaded fasteners but it is only an indicator of the tension. Unfortunately there is no cheap, easy, reliable way to directly measure tension in a bolt but application of known torque gives sufficient control in the majority of situations. It is widely accepted that the majority of torque we put into a threaded fastener goes into overcoming friction in the assembly as only between ...

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