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Fasteners, also known as standard parts in the market, are mechanical components that can hold or bond two or more components together in a mechanical way. This article mainly introduces some common problems of fasteners, and hopes to give you some references.

How to tighten the bolt and nut?

Threaded connections using bolt-nut fits are the most common in fastener applications. To ensure the strength of the connection, self-locking nuts are generally used or additional mechanical locking is used to prevent loosening from occurring. The installation of threaded fasteners is also very simple, as long as there is sufficient torque to achieve preload at the interface, but there are still many people who are unsure whether they should be tightened by the nut or bolt head.

Common problems:

• Should I apply torque to the bolt head or the nut when tightening?
• Is applying torque to the bolt head or the nut the same result?

In some cases, it is perfectly acceptable to tighten the bolt head while holding the nut in place. However, in some applications, tightening the nut is the only viable criterion depending on the application (projection weld bolts or projection weld nuts), the construction of the product itself, and the material and installation conditions.

In some applications you can apply torque to the bolt head or nut and maintain a tight connection; in the following applications, I'm afraid you can only apply torque to one of the components.

• interference fit in the hole of the interference fit, you should apply torque to the nut for installation.

• bolt head and nut have different shapes and diameters When the bolt head and nut have different shapes (such as hexagonal head bolts formula-shaped nuts) or significantly different diameters, it is best to apply torque on the side with the smaller bearing surface. For example, if the head of the bolt is smaller than the nut, the torque should be applied to the head of the bolt. It can be simply understood as a small place to send force, large bearing force.

• different materials When two different materials need to be clamped together, it is best to apply tightening force on the material with the lower coefficient of friction, which means that the torque is applied to tighten on the side with the least possible friction.

• long bolt applications when the torque is applied to the head of a very long bolt, it is very easy to have the problem of torsional coiling, so in this case, applying torque to the nut will help to avoid the problem. There is one such application where the nut is a flanged nut and the bolt head is not, meaning that the friction radius on the nut side is larger than the bolt head side.

Solutions:

If the tightening torque is determined with the nut to be tightened, then an overload problem may occur if that torque is used to tighten the bolt head. Typically, nearly half of the torque is needed to overcome the friction under the tightening surface, so a smaller friction radius will result in more torque entering the threaded joint and therefore an overtightening problem. Conversely, assuming that the torque is determined by tightening the bolt head, if the nut is tightened, which means that the torque is applied to the side with the larger friction radius, this will result in insufficient preload being fed into the threaded joint and may cause a loosening problem.