How to Choose the Right Vibration-Resistant Fastener

Fasteners are designed for all sorts of applications, from heavy-duty construction to mounting a circuit board, and there are almost as many fastener designs as there are applications. The toughest and most secure fasteners have to be used in rugged applications, such as engine mounts, rail cars, factory equipment, cars, or anywhere that constant shaking would loosen most nuts and bolts. Vibration-resistant fasteners are specifically designed to be especially resilient for these applications, but to prevent a joint from failing, you have to know how to choose the right vibration-resistant fastener.

It is easy to imagine fastener applications in which vibration could present a problem. In aerospace applications, for example, a joint failure due to constant vibration could result in disaster. In the oil and gas industry, vibration-resistant fasteners are used instead of welds for equipment assembly and even oil rig installations because they are stronger and last longer. For construction applications such as bridge-building, specific types of lockbolts and blind bolts can provide the type of vibration-resistant joint you need to handle vibration from continuous traffic.

To choose the right fastener for the task, you need to know what to look for in a vibration-resistant fastener.

Sufficient Grip Range and Shear Strength

Two primary considerations when assessing vibration-resistant fasteners are grip range and shear strength.

The grip range is the total thickness that the fastener can handle. The grip is the total thickness of the material being joined, and the grip length is the distance from the underside of the fastener head to the first thread. The grip length needs to be less than the actual grip for a firm joint. The grip range is the difference between the length of the fastener and the width of the material being joined. For a vibration-resistant joint, the grip range needs to allow the fastener to take full advantage of the available fastener threads. The objective is to maximize the tensile strength—the strength of force parallel to the fastener shaft—so it won’t work loose under vibration.

Shear strength is the ability for the fastener to withstand lateral force without breaking. Shear strength is determined by the type of material used for the fastener and the amount of play in the joint. The amount of stress being placed on the fastener is determined by the amount of vibration.

Types of Vibration-Resistant Fasteners

Vibration-resistant fasteners come in various configurations, including blind bolts, rivets, lock washers, lock nuts, hex nuts, and nylon washers, among others. Each design has its value for specific applications, but for lasting performance, we recommend these six types of fasteners:

1. Blind bolts. These fasteners are called blind bolts because they are installed from one side of a joint and are extremely popular for applications that need to withstand heavy vibrations. Designed with a pin and steel collar, when blind bolts are inserted through a pre-drilled hole and tightened, the blind side collapses against the material while the collar is swaged on the facing side to form a joint that is stronger than a weld or rivet.
   
   
2. Structural blind rivets. Similar to blind bolts, structural blind rivets or break-stem rivets have a pin and a slotted sleeve that are inserted through a pre-drilled hole. When tightened, the pin is pulled to collapse the sleeve on the blind side, swage the sleeve on the facing side, and break off the stem once the fastener is tight. These rivets offer more shear strength and pullout strength than many other types of fasteners.
   
   
3. Lockbolts. Typically used in manufacturing and construction, the lockbolt has a pin that is inserted through a pre-drilled hole and a collar that is fitted on the opposite side. When the collar is tightened, the pin is pulled to bring the material together and the collar is swaged into threads in the pin for a permanent joint.
   
   
4. Wellnut threaded inserts. For applications in which mitigating vibration is a concern, wellnut threaded inserts are rubber flanged inserts that are placed in a pre-drilled hole and expand when a bolt is passed through and tightened, creating a joint that can absorb vibration.
   
   
5. Coil thread inserts. As the name implies, coil thread inserts are wire coils that are screwed into a pre-drilled hole. When a bolt is screwed in, the coil expands and exerts pressure on the walls of the hole, creating a strong, vibration-resistant bond. Coil thread inserts are usually used to repair stripped holes, but they are ideal for vibration-proof joints as well.
   
   
6. The Huck 360®. This nut and bolt combination offers a unique approach to vibration resistance. The Huck 360 has a nut made of softer material than the bolt to form a stronger metal-on-metal bond when it’s tightened. It can be loosened like a conventional nut but won’t become loose with vibration.

As you can see, depending on the application, you want to choose different types of materials. With blind bolts, blind rivets, and lockbolts, for example, having a softer material used for the collar creates a stronger metal-to-metal bond with the grooves in the pin. Coil thread inserts are also useful for applying fasteners in softer materials, such as plastic, wood, or fiberglass, because the coil forms a tight joint with the hole in the workpiece, so it won’t pull out.

When it comes to vibration-resistant fasteners, you want to be sure to choose the right fastener for the application, so the joint won’t fail under stress. With so many choices, it makes sense to consult the professionals. At Bay Supply, we have a staff of fastener experts ready to answer your questions and offer suggestions based on years of experience. Feel free to contact us with your fastener questions. And to learn more about rivet nut threaded inserts, be sure to download The Essential Guide to Threaded Nut Inserts.