A caster is an assembly that includes a wheel and a mount. Casters support and make it easy to maneuver carts, racks, dollies and other equipment. Casters come in different materials, wheel diameters, tread widths, load ratings and overall heights to give your equipment mobility in many kinds of work environment.

To help determine which type of caster best fits your needs, think about these questions:

• How heavy are the loads that these casters will need to support?
• Is the working environment wet or oily?
• Is exposure to chemicals or corrosives a concern?
• What temperature range will the casters be exposed to?
• What floor or surface type do you need to maneuver across?
• Are aesthetics or noise reduction a concern?
• Are brakes needed?
• Will the casters be used for powered towing?
• Do you need certifications in CA Prop 65, NSF for food service use or other standards?

Maneuverability: Rigid Casters, Swivel Casters, Kingpinless Swivel Casters

When considering maneuverability, there are two basic kinds of caster: rigid casters and swivel casters.

• A rigid caster, also known as a fixed caster, is only able to roll forward and backward.
• A swivel caster has a raceway that allows the wheel to turn. The raceway is the cylindrical portion of a swivel caster containing the ball bearing track or tracks.

The traditional swivel caster design relies on a kingpin, which is a bolt or rivet that holds the raceway together. In this design, the kingpin is subject to high levels of stress, especially from the shocks that result when the equipment runs into obstacles or when heavy weights are dropped onto it. Because of this, the kingpin is a frequent failure point for traditional swivel casters.

A kingpinless caster is a special type of swivel caster with a raceway that is not held together by a bolt or rivet. Stress is distributed more evenly, which means that kingpinless casters typically last longer than traditional swivel casters. They are recommended for powered towing applications because they can better withstand the stress caused by turning at speed. They are also better at handling shock forces such as rough terrain, obstacles and drops. However, kingpinless casters typically have a higher initial cost than traditional swivel casters.

Rigid and swivel casters can be used in different configurations for different applications:

• The most common caster configuration uses two parallel swivel casters and two parallel fixed casters. This gives the cart good turning and straight-line travel capabilities.
• Carts with only swivel casters are easy to move in any direction, which is useful for maneuvering lighter loads in tight locations, but they are hard to control. Swivel locks on two of the casters can make straight-line travel easier in this configuration.
• Four rigid casters in a diamond pattern can be a cost-effective arrangement. In this configuration, the central pair of casters on the left and right sides is typically slightly taller than the pair on the front and back sides. This makes the cart relatively easy to turn and pivot when the load is arranged over the central fixed casters.

Caster Wheel Materials and Dimensions: General Characteristics

Wheel materials and dimensions are important to consider when selecting casters. What a wheel is made from, and how large or small it is, influences how easily it moves (which in turn influences the ergonomics of the cart) , how durable it is, how much noise it makes and more.

Carts with wheels made from harder materials will generally be easier to get moving than those with wheels made from softer materials. That's because wheels made from harder materials have lower starting resistance, especially as the weight of the load increases. Starting resistance is the force the must be overcome to put the wheels in motion when they're at rest. Wheels made from harder materials also have lower rolling resistance, which means it takes less force to keep them moving at a constant speed.

Wheels made from softer materials are generally quieter and more comfortable to use because they transmit less vibration. They can also help preserve soft floor materials, such as hardwood or tile, which might be damaged by a harder wheel.

Comparing Wheel Hardness: Shore A, Shore D, Brinell

In general, rubber casters are softer than plastic casters, which are softer than metal casters. The hardness of specific casters is rated using three scales:

• The Shore A scale is used for softer rubbers.
• The Shore D scale is generally used for harder rubbers and plastics.
• The Brinell scale is used for metals, which are given a Brinell hardness number (BHN).

Within each scale, higher numbers indicate harder materials.

Wheel Dimensions

The diameter and width are the two measurements that give the dimensions of the wheel. The diameter is the height of the wheel. (The total height of the caster includes the wheel and the mount.)

In general, wheels with greater diameter and width have lower starting resistance and rolling resistance—it's easier to get them moving and keep them moving. They can withstand heavier loads, and they are generally quieter.

However, wheels with greater diameter also give the cart a higher center of gravity, which can make it less stable, especially with heavier loads stacked higher on the cart.

The chart below summarizes how wheel material and dimensions can generally affect equipment performance.