Choosing Fasteners for a Critical Bolted Joint

A critical bolted joint requires more than a simple nut and washer combination, and choosing the proper fasteners can be a challenge. In order to protect against the problem of vibration, a locking nut or retention system needs to used. Depending on the application and whether or not lubrication is present, the best retention system […]

A critical bolted joint requires more than a simple nut and washer combination, and choosing the proper fasteners can be a challenge. In order to protect against the problem of vibration, a locking nut or retention system needs to used. Depending on the application and whether or not lubrication is present, the best retention system could be one of several choices.

Friction-based Fasteners

Some locking fasteners are based on friction. The washer bites into or strains against another washer or surface, creating resistance to loosening. Many fastener distributors, manufacturers and designers hesitate when specifying friction-based fasteners, as vibrations and heavy lubricants can loosen the washers and cause fastener failure. But this type of locking fastener will perform well in applications where low levels of vibration exist.

In most cases, friction-based locking sets cannot be torqued to a specific level. Depending on the design, this type of fastener solution cannot be reused should you need to remove the fastener for maintenance. This type of fastener is affordable and popular in certain types of applications.

Tension-based Fasteners

These fastener sets perform in a similar fashion and effectively lock a bolt into place, but the design utilizes tension instead of friction. A notched washer or nut is fitted against the joint surface in such a way that should the bolt move or loosen due to vibration, the nut or washer will engage a second fastener and lock. The tension created between the first and second nut/washer pieces moving in opposite directions creates an effective lock.

The amount of lubrication does not affect the performance of this type of fastener. Many modern designs of this sort can be reused, making them more valuable. They also tend to go in faster than the average friction-based fastener, cutting the cost of installation. In general though, a tension-based locking fastener has a higher initial price tag than the above type.

Both service a critical bolted joint and protect your application, but one may be the better choice. Think about the amount of vibration the bolt is likely to be subject to and the amount of lubrication present. Choose between low cost friction-based fasteners or high performing tension-based fasteners.