Working with Fasteners requires the utmost care at time, while others times you need to apply brute force. A common Fastener question that workers in many industries ask applies to torque. When tightening Hex Bolts or other Nuts and Bolts, are you better to apply torque to the nut or the bolt head? Is one method more likely to result in breakage? Or are both equally effective? These questions may also apply to Hex Head Cap Screws.

The answer depends on your application and the condition of the materials being fastened.

In many situations you can apply torque to either the nut or the bolt head. Both will result in a tight connection and neither will avoid breakage more often (that occurrence can be avoided through other means). In certain circumstances, however, you will need to torque one and not the other. These situations include:

Holes Are Producing an Interference – If the holes you are bolting through (whether existing or drilled for the purpose) provide an interference, you are better to apply torque to the nut.

Nut and Bolt Head are Different Diameters or Shapes – When the nut or bolt head are different shapes (hex head with a square nut, for instance) or significantly different diameters, you are best to apply torque to the side with the smaller bearing face. This also applies when the hole diameters are different. It is generally recommended that you apply torque to the component opposite the smaller hole.

When Clamping Two Different Materials Together – It is always better to apply torque on the component that is against the material with a lower frictional coefficient. If you are clamping together different materials and you know which one will produce less friction, it is best to torque that side.

Long Bolts Are Being Used – When torque is applied to the head of a very long bolt, you may see the effects of torsional wind-up. Applying torque to the nut in this situation will help to avoid that issue.

There will be many instances where you can apply torque to either the nut or the bolt head. But if one of the above situations applies, remember to follow the guidelines for a better fit and more durable installation.