Cable Bolts

Setting the torque
Engineered joints require the torque to be accurately set. The clamp load produced during tightening is about 75% of the fastener’s proof load. Over tightening will damage threads and stretch the bolt, ruining the joint’s strength; see Hooke’s law.

If the hardware is Cadmium plated, or lubricated (or both) the torque is reduced by 15 – 25% to achieve the same clamp load. Specialty coatings exists that allow for a reduction of 50% in torque (compared to non-plated, non-lubricated hardware) to achieve the designed clamp load. Cadmium plated fasteners are no longer produced due to the toxicity of the metal.

Torquing the bolt is notoriously inaccurate. Even with a calibrated torque wrench large errors are caused by dirt, surface finish, lubrication, etc. The turn of the nut method is more accurate, but requires additional calculations and tests for each application.

There are more expensive tools for accurate torque setting, like ultrasonic meters, but they are out of reach of most shops.