What is a Locking Washer and Why Would You Use One?

Washers, nuts, and screws are vital for holding many things together, from industrial machinery to household items like string trimmers. They are very efficient most of the time, but when the nut doesn’t hold in place, it’s not necessarily a part failure. Vibration is the main culprit that causes nuts to loosen dangerously. A standard washer helps keep a screw in place and distributes the pressure from the nut evenly over a wider area, but what is a locking washer, and why would you use one?

How Does A Lock Washer Work

The purpose of a locking washer is to hold a nut in place, but how does it work? These unique pieces of hardware do a completely different job from a typical washer to work together. However, it is essential to use them in the correct order. An ordinary washer exists to keep a screw in place and help prevent other hardware from sinking into a soft surface like wood. By distributing pressure, it prevents holes and further damage. These can go on the nut or screw side, and sometimes it is used on both. The wide, flat, round disks of standard washers have a round hole in the center and belong between the nut or screw head and the surface you put a screw into. The greater surface area prevents the tension from crushing objects that are screwed together. As a general rule, the larger the washer, the better it distributes weight. A locking washer is usually smaller than the flat variety, and it must go on top of a regular washer when you are using them together on the nut side. If you place it under the broad, flat surface of the other washer, it can’t do the job it was built for. The unique shape of locking washers creates tension on the nut, which prevents it from loosening. Both the standard and lock washers vary in size and thickness depending on their intended uses. You will often find these made from aluminum, bronze, or phosphor bronze alloys, carbon steel, and stainless steel. Like the shape and size, the material affects how a locking washer is used, with tougher alloys generally taking more torque.

What Types of Locking Washers Are There

There are five main types of locking washers. Some are specialty pieces like the Wedge lock washers, and others are more generalist, like the spring style. The shapes vary significantly, but every one of the locking washers on the list below can help secure your screws, bolts, standard washers, and nuts in place.

• Dish and Dome- The dish and dome-style washers have a concave and convex face. These look a lot like a standard washer and disbursing pressure over a larger area, but they are curved. The dish style is used for lower torque, while the dome can handle greater forces. Unlike the Split washer, you can sometimes use these to replace an ordinary washer because they create tension and weight distribution.
• External and Internal Tooth- An external tooth lock washer looks like a gear, while an internal tooth washer looks like an inverted gear with the teeth inside, though it is also possible to have both sets of teeth. These protrusions bite into the surface or the bolt to hold everything in place and work best with larger diameter hardware.
• Helical Spring (Split)- Helical Spring washers or split washers resemble a slightly flattened chainmail ring of a very short piece of a spiral. They are true to their name and do not make a continuous circle. As a nut tightens down on top of this style, it flattens, creating the necessary tension. Split lock washers are the most commonly used style and the type most people think of first. It is important to note that too much torque can flatten this style, effectively making it a simple, standard washer with no added value.
• Pyramidal- A Pyramidal lock washer looks like a combination of the dome and internal tooth styles. Typically they only have about four teeth, and the ‘dome’ is steeper, more pyramid-like rather than a shallow semi-sphere.
• Wedge or Disc- According to Huyett, the disk or wedge lock washer is intended as a “single-use, heavy-duty, self-locking washers composed of a pair of washers featuring cams on one side and nonslip ridges on the other.” These two pieces lock together thanks to their unique texture and hold everything in place.

When to Use Locking Washers

There are several times when a lock washer is a perfect accompaniment to your project. First, household appliances, particularly washers and dryers, tend to vibrate and move a lot. By adding tension to your nuts, they are less likely to work themselves loose. Likewise, you could look at adding a Helical Spring locking washer to the bottom of your weed wacker or lawnmower where the blades attach. However, it is essential first to check and ensure you have enough room to do so safely. The most common use for locking washers is in transportation. Whether it is a car, plane, motorcycle, truck, or boat, properly tight nuts and well-fitted screws are critical. Without suitable hardware, your vehicle can literally fall to pieces. Torque wrenches are often used for working on motor vehicles because tension is so vital. The added assurance from a lock washer can help extend the working life of connected pieces. Loose pieces can rattle around, and hardware in motion can even fly off, causing more damage to the machine. Plus, it’s nearly impossible to find your missing hardware when it falls off of a moving vehicle.

How Not To Use Lock Washers

A locking washer can help secure most projects, even though they are more common in the transportation industries. That said, there are times when you should never use lock washers. For example, when a screw or nut doesn’t fit properly because it is too large or too small, no amount of tension will make it safe. As Hunker points out, you should not use lock washers to tighten overlong nut and bolt combinations. In this case, you’ll need new, better-fitting hardware instead.

Final Thoughts

Choose a locking washer when you’re concerned about vibration or loose hardware. You will often see these on marine equipment because a failed screw and nut on the water could turn into a life or death situation quickly. Fortunately, while there are a million great uses for lock washers, you won’t always need them. Especially when your project is unlikely to move much, there’s no need for extra parts.