Axle bolt and nut: The axle bolt locates the wheel into the caster yoke.Common bearings used for caster wheels include: roller bearings, tapered roller bearings, ball bearings, precision ball bearings, Delrin and self-lubricating sleeves. There are numerous bearing options depending on the wheel design and the application being considered. Wheel bearings: Most caster applications require the wheel to function with a bearing.The proper wheel selection is dependent on application factors such as floor conditions, load, rollability, speed and climate. There are numerous grades of all of these materials. Wheel: Caster wheel materials include elastomers (rubber and polyurethane), phenolic, nylons and even steel.There are also hydraulic and elastomeric springs. The typical spring mechanism is a coiled steel spring. Spring mechanism: Certain casters serve a shock absorbing or vibration dampening function so there needs to be a spring mechanism in the caster design.The yoke is also known as the fork, rig or housing. The yoke, working with a swivel head allows the caster wheel to operate in a 360 degree manner. The caster yoke serves to hold the wheel in place. Yoke: The part of a swivel or rigid caster and can be considered a frame.Grease fittings may also be known as "zerks." Grease fittings serve to inject grease into the axles, caster raceways and wheels. Bearing designs include ball bearings and raceway bearings. The swivel action of a caster depends on bearings and lubrication. A swivel caster allows for 360 degree directional movement. Swivel head: A rigid caster allows single back and forth direction.Casters may also have a bracket allowing the caster to be mounted to vertical panels. A caster stem may screw into place or ‘snap’ into place. A caster top plate allows the caster to be bolted to the underside of the equipment. Mount: Casters mount to equipment or carts in three common manners.The key elements of a caster include the following: The key dimensions to consider when determining the proper type of caster and caster size for a particular type of equipment and application are its overall height, swivel radius, and swivel offset (see Caster Dimensions diagram). They can be a one piece construction or a two piece construction that is riveted or welded. They are rated at the same capacity as the swivel casters for safety reasons. Rigid casters tend to be stronger than swivel casters. This style of caster only allows forward and backward movement. Some common types of stems are threaded, round or square with mounting holes, friction ring & expandable stems. Stem casters: This type caster can have various stem styles to be used to mount the caster to a unit.Top plates are offered with various hole patterns to match numerous types of mounting requirements. Most mounting plates contain four holes used to bolt the caster to the unit. Plate casters: This is the most common type of means to mount a caster to a unit and is sometimes called the top plate.The hole in the rivet can accept a bolt or a customized stem for any type of mounting requirement. Hollow Kingpin casters: This type of caster has a tubular rivet that holds the caster together.This design is extremely durable and can be used in abusive applications and shock load applications where kingpin type casters may fail. The raceways are a one piece construction forged together. Kingpin-less casters: This caster does not have a bolt and nut kingpin.Locking casters: There are several devices that can be added to casters to prevent the wheel from rotating or the swivel assembly from turning.The different types of swivel casters include the following: They can have one or two sets of raceways that allow the caster to swivel 360 degrees under a load. This type of caster allows for movement in multiple directions. Casters comprise two major categories: a swivel caster pivots around a kingpin, so it rotates as well as rolls, while a rigid caster has its wheel mounted in a fixed frame, or rig, and only rolls.