Should I Tighten the Bolt or the Nut in a Bolt-Nut Connection?

In a threaded connection, how should I choose between tightening the nut and tightening the bolt?

In a threaded connection, the question of whether to tighten the nut or tighten the bolt does not need to be considered for riveted rivets, rivet nuts, welded welded nuts, welded bolts, etc. Also, when using studs, there is no need to consider this issue, only the nut can be tightened.

Whether to tighten the bolt or the nut is usually considered in a bolt-nut connection. In most working conditions, when there are no special requirements, the nut is mainly tightened to tighten the connection. However, in special cases where the working space is limited and the tightening tool cannot be used, the nut will be clamped first, and then the bolt will be tightened to achieve a tightened connection.

What is the difference between tightening the nut and tightening the bolt?

The main difference between tightening the bolt and tightening the nut is that the friction coefficient is different, which will lead to a difference in the preload force of the bolt under the same torque. If the preload force needs to be strictly controlled, there will be a difference between the two. However, when the friction coefficient and the support surface diameter are the same, the tensile stress and torsional shear stress of tightening the bolt and the nut are the same, and it is okay to tighten either one. From a habitual point of view, people screw nuts more often.

There is no relevant standard that says that bolts or nuts must be screwed. In terms of force-applying tools, a shorter socket wrench can be used to screw bolts. When screwing nuts, the exposed length of the bolts needs to be considered. The socket wrench generally used is longer, which may increase some costs. However, in most anti-rotation tooling designs, long socket wrenches are also used to screw bolts, so in this regard, screwing bolts and screwing nuts are not much different.

The reason why people usually screw nuts more is that if the bolts are not aligned, there will be friction between the screw and the prefabricated hole, thereby increasing the friction torque and increasing the input torque, while screwing nuts does not have this problem.

In short, screwing bolts and nuts are the same in most cases. From the perspective of convenience, nuts are mostly screwed. Unless it is inconvenient to screw nuts under special working conditions, then choose to screw bolts. Of course, it is best to specify when designing whether to screw nuts or bolts in order to achieve the design preload requirements.