- Huyett Marketing Department
- 01/13/2022
Threaded nuts are one of the most versatile and ubiquitous fasteners. Nuts — when paired with a threaded bolt, screw, or stud — provide the clamping force required for a secure and long‑lasting joint. Because nuts are inexpensive and easy to install, they are used in almost every manufacturing and construction industry. However, nuts have one significant weakness; they tend to loosen over time when the joint is exposed to vibrations, cyclical changes in load, or fluctuating temperatures.
How to Keep Nuts from Loosening
When a nut is installed, it is torqued so the nut and threaded shaft are in tension (preload force) and the parts being fastened are in compression (clamping force). The preload force pulls the threads on the nut and bolt together, reducing the nut's tendency to slip. And while the preload force helps prevent vibrational loosening, it may fluctuate if the joint experiences excessive vibration or temperature changes that allow the threads to move relative to each other.
There are many solutions to the problem of self‑loosening nuts. One of the simplest is the jam nut, an additional nut screwed onto the shaft above the first nut. Jam nuts are typically half the height of a standard hex nut, allowing for a shorter shank on the mating bolt or screw and a lower profile once installed. Another option is the castellated nut, which has slots cut into its top through which a cotter pin or wire is inserted. The pin goes through the nut and the shaft, preventing the nut from self‑loosening.
However, both jam nuts and castellated nuts increase manufacturing and maintenance complexity, making them unsuitable for some applications. For this reason, many manufacturers prefer to use self‑locking hex nuts, lock washers, or bearing lock nuts, depending on the specific needs of their project.
Hex Lock Nuts
A
hex lock nut is similar to a standard hex nut with an elastic or metal insert. When the nut is installed, the insert deforms around the threads, creating intentional interference.
Hex lock nuts are also called prevailing torque nuts. Prevailing torque is the force needed to install the nut before it exerts a clamping force. The hex lock nut's insert increases the prevailing torque required to install or remove the nut, helping it resist loosening.
How to Use Hex Lock Nuts
Hex lock nuts are installed in much the same way as standard hex nuts.
- Select a hex lock nut with a matching diameter and thread to the bolt or shaft it will be installed on.
- Hand‑tighten the nut as far as possible; you may not be able to hand‑tighten as much as with a free‑spinning nut because hex lock nuts require more prevailing torque.
- Use a wrench to tighten the nut until it is tightly seated against the surface of the mating part. It is normal for a hex lock nut to require more force than a non‑locking nut.
Lock Washers
What is a Lock Washer?
Lock washers are a variation on the standard washer. As we saw in the previous section, preload force helps to keep the nut and bolt in tension and the joined parts in compression, ensuring that the mating threads are in contact. But the preload force can change with vibration and varying load on the joint. Lock washers exert an additional force to keep the nut and bolt in tension.
This is usually achieved by designing washers that resist compression by clamping forces; they act as a spring pushing against the joint so the threads remain in contact through vibration and load changes. Lock washers also increase the friction between a nut or bolt head and the mating components, reducing their tendency to rotate and loosen.
Split Lock Washers, which are also called helical spring lock washers, are metal rings split and twisted so the cut ends no longer align. When compressed, they are squashed flat and exert force to regain their original shape. In addition to acting as a spring, a split washer may penetrate the surface of softer metals, increasing friction that resists turning. Split lock washers are suitable for many applications, but they may not be the best choice for applications that are exposed to extreme vibration.
For more challenging environments that experience extreme vibration or loading variations, washers that use alternative methods to maintain preload are preferable.
Belleville Washers, also known as conical spring washers, are cup‑shaped washers that resist compression. Belleville washers can generate more preload than split lock washers and they can be stacked to increase stiffness. Another option is
Curved and Crescent Washers, which use a curved or "wavy" shape to resist compression.
Disc‑Lock Washers, also known as wedge lock washers, work on a different principle to spring‑type washers. Disc‑lock washers are used in pairs. Each washer has inclined cams on one side and high‑friction non‑slip ridges on the other. The cam sides are interlocked during installation, preventing the two washers from rotating against each other. The non‑slip side prevents the nut from rotating against the washer. If the nut attempts to turn under vibration or heavy loading, the interlocking cams push the washers apart, increasing the preload force and causing the nut to return to its original position.
How to Use Lock Washers
Lock washers that act as springs are installed in the same way as flat washers:
- Choose a lock washer that meets the size and torque requirements of your project.
- Place the lock washer between the nut or bolt head and the part's surface. For Belleville washers, the cup should point towards the connection and away from the nut or bolt head.
- Tighten the fastener to the flat load suggested in the manufacturer's instructions. Flat load is the force required to flatten the washer. A washer with too little load provides insufficient spring force and friction, and an overload washer may be permanently deformed.
To install a Disc‑Lock Washer:
- Insert both halves of the washer onto the shaft. Ensuring the jagged cam sides are in contact with each other and that the non‑slip sides will connect with the part's surface and the nut or bolt head.
- Tighten the fastener until the washer halves are firmly in contact.
Bearing Lock Nuts
What is a Bearing Lock Nut?
Bearing lock nuts are used to secure bearings and other components axially onto a shaft. They're also known as shaft lock nuts or bearing retaining nuts. Unlike hex lock nuts, bearing lock nut installation requires a special tool: a spanner wrench or lock nut socket.
There are several different types of bearing lock nuts, but one of the most widely used requires a bearing lock washer and keyed shaft. The washer features multiple angled tabs on the external diameter that can be folded into slots in the bearing lock nut's chamfered edge. A tab on the internal diameter locks into the keyway or a slot on a bearing adapter sleeve to stop the washer from rotating.
The bearing nut is threaded onto an axle or a bearing sleeve until the washer is compressed. Then, one of the tabs is bent into a slot on the nut to secure the assembly in place. Additionally, a set screw may be used to fix the bearing nut in place.
Together, the bearing lock nut and bearing lock washer counteract changes in the preload force and prevent the bearing from loosening when the axle is torqued or vibrated.
How to Use Bearing Lock Nuts
Installation instructions depend on the bearing lock nut's design, but the process is typically as follows:
- Slide the bearing onto the shaft or adapter sleeve.
- Slide the bearing lock washer onto the shaft with the tabs facing away from the bearing.
- Screw the bearing lock nut into position with the chamfer facing the bearing lock washer.
- Tighten the nut with a spanner wrench or lock nut socket. Use the manufacturer's recommended torque and avoid overtightening. Ensure that the bearing is not pushed out of position when tightening the nut.
- Bend a lock washer tab into a slot on the nut to lock it in place.
Where to Source Hex Lock Nuts, Lock Washers, and Bearing Lock Nuts
Huyett stocks a wide range of high‑quality lock nuts and other retaining hardware, including:
Visit huyett.com to explore our full line of nuts washers, and retaining rings and to see product specs and buy online, or
contact our friendly, knowledgeable Sales Team today.
