A caster is a mechanism used to support and maneuver a range of mobile items such as carts, racks, dollies, and other material handling equipment. A caster refers to the whole apparatus, including framework, attachment unit, and the wheel itself. Casters are used in a variety of industries including health care, manufacturing, commercial, institutional, and food service.
Casters are often selected for their mounting system, which is typically a plate or stem attachment mechanism. A mounting plate, measured in inches, refers to the flat base (usually with four bolt holes) that forms the top of the caster and permits attachment by bolting or welding to a flat surface. A stem caster is attached to the surface with a central bolt, measured in inches. The stem can be threaded and comes in shapes such as round or square.
When selecting an appropriate caster, there are several features to consider. A caster's maneuverability can range from rigid to a 360-degree swivel. Rigid casters provide movement in a back-and-forth motion, allowing for more controlled movement than a swivel caster. Swivel casters allow for a 360-degree shift in direction, for more ease of maneuvering than rigid casters. Casters can have a lock with a pin-type plunger for each wheel, which can be locked at various angles. Some casters have a brake with a foot- or hand-operated lever that compresses the caster frame against the hub center, or wheel, to prevent rolling.
Tread material is also important in caster selection. Generally, wheels with hard tread material have a higher load capacity and roll easier than soft tread wheels, which provide quieter operation and a cushioned roll. Hard tread wheels are used for manufacturing applications where steel grading, metal debris, or rough floor surfaces exist. Polyurethane is one of the hardest, most durable materials, while rubber is typically softer, for noise and shock reduction. A durometer, often used in caster tread selection, is a scale for measuring the hardness of a wheel material, and is measured from 0 to 100, with higher numbers representing the hardest material. Caster tread materials are selected for their ability to perform within surface, stress, temperature, environment, and operating conditions. Wheel tread material can be a combination of materials, or a single type. It can be formed as one solid piece, or molded, bonded, or mechanically locked to a core.
Load capacity for individual casters is expressed in pounds. Casters have the ability to support a wide variety of load capacities, from less than 100 pounds to over twenty thousand pounds. The application range for these capacities is different for various manufacturers. Wheel tread width, which measures the horizontal tread width in inches, must also be considered for load capacity. Generally, a larger width supports a heavier load, rolls easier, and distributes the load for better floor protection.
A final consideration for caster selection is wheel diameter, which is expressed in inches, and refers to the vertical measurement of the tread from top to bottom. The diameter of the wheel affects its ability to carry a weight load over a variety of surfaces and conditions. Generally, casters with large wheel diameters are able to support heavier loads. Wheel diameter is different than overall height of a caster, which refers to the total vertical distance from the floor to the top of the mounting plate, or the base of the stem of the caster.