Musculoskeletal injuries dominate workplace injury statistics. Roughly two thirds of all reported injuries each year fall into this category. Add to this the aging and increasingly obese workforce in the U.S., and there is an obvious recipe for even more work injury problems in our future. Manual material handling, and specifically pushing and pulling wheeled devices, is a major contributor to the injury statistics. Carts, dollies, and platform trucks used to move material are ubiquitous in most workplaces, yet little thought is given to the critical ergonomic factors. Carts and dollies can be either our friends or our enemies, depending largely on the casters and wheels.
For those in the industry, the term "caster" is common jargon. For those in other industries, the term may confuse. One relatively easy way to be sure the audience understands what is meant is to consider desk chairs that roll. They roll on casters, albeit small ones. Modern luggage frequently rolls on very small casters. Grocery carts feature four of them. Bed frames frequently rest on them. Casters are also very common in the workplace.
Casters are structures that house one or more wheels. The structure may rotate about a vertical axis (termed "swivel") or keep the wheel in a fixed direction (termed "rigid"), and can vary greatly in size. Industry differentiates casters by size, using the diameter of the wheel(s), as the major differentiator. Secondarily, industry uses capacity, or amount of weight or load one caster can support. Casters mount to the larger objects they support via bolted plates, threaded stems, or may simply be welded in place.
Wheels vary in more ways than most recognize. The glaring differences are in size and composition. Furniture casters generally have very small wheels, while wheels on industrial carts tend to have larger diameters. Not only are there variations in diameter, but also in tread width. Wider wheels normally have higher load-carrying capacities than narrower wheels.