Flat vs. Lock Washers — What You Need to Know Before Buying Washers

A washer is a machine component that features a thin plate with a hole. It works with a screw fastener to keep a screw from loosening or experiencing too much pressure. There are many types of washers — including flat, lock, structural and beveled — that are built for different needs and situations.

What Are Washers Used For?

This piece of hardware is almost always used with fasteners to prevent any moving or corroding. Lock washers are explicitly built to lock nuts or bolts in place. An essential function of washers is providing a smooth surface for nuts or bolts, making them less likely to loosen.

Washers significantly increase a product’s life span through load distribution since less pressure is on the fastener, which leads to greater support and less chance of failure. They can also be a wear pad that protects expensive parts while remaining cheap to replace. This function works great with washers made of softer material like plastic, since they’re excellent at absorbing vibrations.

Some assemblies are made to move when the bolt is tight. A washer is used in this case to reduce the friction between materials since the moving parts are more likely to wear out quickly if they were to rub against each other.

Washers are critical in a plumbing system for a couple of reasons. First, they evenly distribute the pressure throughout the entire pipe to prevent strain. Second, washers used with faucets act as a seal to stop leaking.

An underrated benefit of washers is that they reduce the friction of parts when they are tightened or loosened, making them easier to break free from a tightened bolt. Washers aren’t a one-size-fits-all piece of hardware. These uses aren’t exclusive, but rather, they work in a combination of multiple services to achieve the best results.

Flat Washers

This type of washer is the most commonly used and is great for protecting the surface of a mating part from damage. Flat washers are often used as general-purpose parts that spread the clamping load from a screw or nut to a more extensive area.

Flat washers are usually available in a variety of materials, including brass, nylon and steel. There are different types for many applications, including:

While they are simple in form, flat washers' usefulness in various applications makes them invaluable for construction projects. For example, fender washers work great in automobile, panel and plumbing applications since they distribute loads to a wide surface area. USS flat washers step it up a notch by offering an even greater inner diameter and are made for a wide range of applications from manufacturing to repair and maintenance.

The main takeaway for flat washers is their load distribution is one of the most valuable parts of using this piece of hardware. However, do not underestimate flat washers' importance in other applications.

Lock Washers

These washers are very similar to spring washers and lock fasteners into place to add an extra level of security. They’re typically attached to the nut side and used in transportation applications like the automotive and aircraft industries. These applications commonly involve significant vibration, which is why you want parts locked into place.

Lock washers still distribute the weight of bolts, but their locking action prevents the vibration from machines from loosening the fastener. They work by applying a spring force against the bolt or nut head. Any flattening or stretching of parts is likely to be much less than the compression of the spring washer, so the fastener won’t loosen much.

Vibration-resistant washers are another common term associated with lock washers, but there are some differences between the two. While lock washers resist torque or loosening, a vibration-resistant washer is sprung, so as the joint moves, the preload takes effect.

There are different kinds of lock washers, but they all have the same purpose — to stop any attached part from moving. Oftentimes they’re combined with other pieces of hardware, so flat and lock washers aren’t exclusive by any means.

Other Kinds of Washers

Additional washer types you may encounter include: 


  • Beveled: This washer is an angled piece that compensates for uneven surfaces in structural applications. A flat washer wouldn’t work for these situations because the surface is nonparallel, which would make for a loose connection. Beveled washers are sloped to one side, so they work best in construction applications.
  • Fender: These washers help distribute the forces of bolts or nuts to a wider surface because of their oversized diameter. This distribution works better for thin or soft materials, which is why fender washers are popular in the automotive and plumbing industries.
  • Metric: Metric washers are the same as flat washers, but with a different sizing chart. They serve the same function as their counterparts and are made of the same material. The metric measurements can be useful for many workers across the world.
  • Finishing: These washers are placed on the outside of a product, which is why they have a more attractive appearance to present a clean, sleek look. A decorative appearance is oftentimes important to a project’s success, which is when this type is needed.

Purchase Standard or Metric Washers From FMW Fasteners

What you need to know before buying washers is that the type you require depends on the application. Understanding the purpose of each washer and what it does to parts is an important first step, and knowing how to apply that knowledge to your situation is equally important. 

Whether you need flat washers vs. lock washers, remember the two are often combined in applications and actually work better when used together. It’s best to contact a professional if you’re in doubt about what your next step should be. We have the expertise and in-house resources to service any need or answer any question! Here at FMW Fasteners, we pride ourselves on providing the perfect mix of product quality and a customer-friendly experience.

Quality is in everything we do, from choosing the right product to fast delivery. See what makes FMW Fasteners the leader in washers and achieve quality results for your construction project. View our entire standard or metric washers collection to get started today.

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