Casters – A Helpful Guide

The following is VERY basic information about casters and caster wheels. You may find it informative.

A wheel and a caster are not the same thing, but often these words are used to refer to the same object. When a customer uses the words, “wheel” and “caster” interchangeably, it often creates confusion. Here is the difference: A wheel is a round object that rolls. A wheel rotates on an axle or shaft that passes through the center of the wheel. A wheel can be solid or spoked. Wheels made of just one material include solid all polyurethane wheels, steel wheels, V-groove wheels, hard rubber wheels, polyolefin wheels, phenolic wheels, nylon wheels and high temperature wheels. Wheels that are made essentially of just one material are almost always solid rather than spoked design.

Wheels that are made in a spoked design usually have a tire molded to another material. Most of the time tires are molded to a solid core which is the center or circular disk supporting the tire. Wheels with a solid core tend to be stronger than wheels that have spokes for a center.

The phrase “mold-on wheels” refers to wheels that have a tire molded onto another material that comprises the center of the wheel. Most of the time the center or core of a wheel is made out of one of the following materials: aluminum, iron, steel, nylon or polyolefin.

The tire that gets molded onto the center of a wheel is usually made from rubber or polyurethane. Rubber tires are made from many different compounds and in many durometers (hardness). The same is true of polyurethane tires. When selecting a wheel it is rare that any consideration is given to the proper tire compound or hardness for a specific application.

Most people choose a wheel on the basis of its rated capacity or its diameter. We have included on our web site a Tips Section called "Factors to Consider Before Selection", which describes most of the major factors one should consider before making a selection. When you do not select the proper wheel for your special application, it will not perform as efficiently as it would had you chosen the right wheel.

Unfortunately, most sales people who sell wheels know too little about them. Our staff is a valuable resource ready to assist you in the selection of the right wheel for your specific application. They have a vast amount of product knowledge and experience in wheel applications.

Now that we have explained what a "wheel" is, let us distinguish it from a "caster". All too often, customers call and say they want to buy "wheels" when in reality, they wish to purchase "casters". So, what is a "caster"?

To start with, one component of a caster is a wheel. Once a wheel is installed in a frame it becomes part of a caster. The frame is often called a caster bracket, rig or fork. All of these words are used to refer to the frame which houses or holds the wheel. The major components of a caster are the wheel and the frame in which it is held.

A caster frame can be either a swivel or a rigid frame. If the frame is a swivel type, then with a wheel installed, it is called a "swivel caster". A swivel caster is capable of rotating 360°. A chair caster or a caster on the bottom of a furniture mover's dolly, are examples of a swivel caster that most people are familiar with.

If the caster frame is rigid, then with a wheel installed, it is called a "rigid caster". A rigid caster is primarily utilized for straight line travel, meaning rolling forward or backward.

In most instances, both a swivel caster and a rigid caster have two "legs". One leg is on each side of the wheel that is installed in the caster frame. The wheel is held in place between the legs of the caster frame by a bolt or axle. Above the legs on a swivel caster is the swivel bearing, which allows a swivel caster to rotate or turn 360°. Above the legs on a rigid caster there is no swivel bearing because a rigid caster is designed only to go forward or backward.

A wheel held between the legs of a caster frame is the lowest part of a caster because its function is to roll on a floor surface. The top of a caster is used to attach the caster to the equipment. There are many ways to attach a caster to a piece of equipment. The most common means is a mounting plate, often called the top plate. The mounting plate on a swivel caster is connected to the swivel bearing and to the legs below the swivel bearing. On a rigid caster the mounting plate is connected directly to the legs, forming a "U" shaped frame to hold the wheel. Most mounting plates on casters contain four holes used to bolt the caster on. Sometimes casters are attached by welding the mounting plate of the caster to the equipment.

Some of the other popular ways to attach a caster to equipment include the following: an expandable rubber stem to insert into tubing; a round or square solid metal stem, also inserted into tubing; an octagonal shaped stem with cross drilled holes to be bolted to angle iron legs; a threaded stem to either go into a tapped hole or to pass through a hole and held in place with a lock nut. There are many other means to attach or fasten a caster onto equipment. When you call for assistance in selecting a caster, it obviously helps if you know which means of attachment you want. We can be very helpful if you are at least familiar with where the casters are to be attached and the kind of equipment the casters are going to be attached to.

A typical piece of equipment supported by casters has either four swivel casters or a combination of two swivel casters and two rigid casters. The main purpose of having four swivel casters is that the equipment can be moved in any direction-forward, backward and sideways. This caster configuration is especially useful when you have to move castered equipment when there is little space to maneuver. When your application requires that the equipment travel in a straight line, such as down an aisle, it is easier to control the direction if there are two swivel casters used in combination with two rigid casters. Most of the time if there is a handle to push or pull on the equipment, it is located on the end where the swivel casters are located. The one exception to this rule would be if the weight to be moved was so light that you could still easily steer from the end where the rigid casters are located, such as on a shopping cart in a grocery store.

There are applications where more than four casters are needed to support a piece of equipment. One example is a piece of equipment so large that it needs to be supported in the center as well as on the four corners. In addition to size, sometimes the application necessitates the use of more than fours casters. An example of this would be the "U" shaped narrow tilt cart used in grocery stores to bring boxes of food from the warehouse into the store aisles to be put onto the shelves. The two rigid casters in the middle are taller than the four swivel casters in the corners. This enables the long narrow tilt cart to maneuver in confined spaces and still go in a straight line down aisles without difficulty.

The large number of caster applications and the many factors to be considered, are two reasons our knowledgeable and experienced staff are a valuable resource. They can assist you in selecting the right wheel and caster.

It is our view that you are not purchasing mere casters or wheels. You are buying a product that must work for you. The internal handling of materials is an expense. Properly designed wheels and casters can reduce this expense.

Caster City is your source for "Quality Casters and Caster Wheels".