Shoulder washers explained

What are shoulder washers?

A shoulder washer is used to insulate fasteners, wires or shafts from moisture and electricity.

This guide is designed to answer your questions about this unique washer, covering these topics:

• Bushing vs. washer
• Where insulating shoulder washers are used
• Types of shoulder washers
• Plastic shoulder washers: dielectric strength

It has many names you should become familiar with to prevent confusion:

• Bush washers or bushing washer
• Step washers
• Shoulder bushing or shoulder bushes
• Shouldered washers
• Sleeve washers
• Insulation washers

Bushing vs. washer

You’ve heard these as two separate words, but what exactly is the difference? Both are essentially hollow cylinders. Bushings are a type of bearing that insulates both moving and stationary parts. You’ll usually find bushings used as a casing for a shaft, hinge or pin or in electrical applications, as an opening for a conductor to pass through.

A washer is a flat disk installed underneath a nut that distributes pressure. A shoulder washer gives you both a washer and a bushing.

Where insulating shoulder washers are used

Wherever electrics are involved, you’re likely to find a shoulder washer in use. You should avoid using them in humid environments. Most industries rely on them, including:

• Electronic equipment
• Automotive
• White goods
• Construction
• HVACs
• Electrical
• Fabrication
• Manufacturing
• Furniture
• Vending & ATMs

Types of shoulder washers

Below are the different styles of shoulder washers and their uses.

Ideal for white goods

Components exposed to high temperatures, such as found in consumer appliances, can benefit from this washer:

Ideal for PCBs

These washers act as an electrical insulator by preventing metal-to-metal contact:

Plastic shoulder washers: dielectric strength

A plastic shoulder washer can rightly be called an electrical insulating sleeve washer. A nylon shoulder washer, for example, has outstanding resistance to not only abrasion and most chemicals, but also high voltages. This is why nylon is often used in electro-mechanical components.

Most plastics are poor conductors of electricity, resisting a current flow. This is dielectrics, and why plastics do such an outstanding job as insulators. Plastics are common materials for wire coatings, cables, switches and other electrical applications.

When voltage is applied and increased, the electrical properties of plastics begin to break down, which lowers their resistance.

A material’s dielectric strength tells us its ability to store electrical energy. It’s also a measurement of a material’s dielectric breakdown resistance under an applied voltage. Dielectric strength is expressed as volts per unit thickness and tells you how effective the material is as an insulator.

The higher the value, the more electrically insulating a material is. These plastics all have excellent dielectric strength:

Dielectric strengths

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