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World Casters & Equipment Manufacturers  
Caster Warehouse Inc, A Division of World Casters & Equipment Mfg
casters, wheels, carts, dollies, hand trucks  
Supplying the Southeast with casters for every application imagineable

Atlanta Based Caster Warehouse, satisfying the needs of the United States
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Common Caster Terms

Here is a list of common caster terms and definitions to help you understand the common parts of a caster as well as key terms used in the industry.

(Highlighted words can be clicked on to jump to the definition of that term.)

Expanding Adapters
Hub Length
Inner Diameter
Load Capacity
Overall Height
Outer Diameter
Position Lock
Quick Change Plate
Rigid Casters
Side Thrust
Swivel Casters
Swivel Offset
Shock Load
Thread Width
Wheel Diameter


Axle: A bolt that is placed through the bearing and attaches a wheel to the Forks of a Caster. Some axles have Zerk grease fittings on them to allow lubrication of the bearing without removing the wheel from the forks. These are known as Zerk Axles. Matching nuts are always sold with the axles.

Bearing: A set of rollers or balls that are encased in a track or Raceway that fit inside a wheel or in the Swivel section of a caster. For wet applications a Delrin Bearing (Plastic) can be used where non-stainless steel roller or ball bearings would rust. Stainless steel bearings are available but can be very expensive. All bearings can help reduce the friction caused when a wheel rotates while under a load. Bearings reduce the effort required to push a cart.

Brakes: Brakes are designed to stop the rotation of the wheel on a flat level floor. Should not be used on an incline, as they are not made to hold the entire weight of the cart. Most brakes engage on the tread of the wheel but the pedal actuator can be located either on the side of the fork or over the tread. Some brakes are designed to work on both the wheel and the raceway at the same time. These brakes are called total lock brakes because they stop the caster from moving completely.

Bushing: A piece of round tubing that can be made of Nylon, Delrin (plastic), sintered steel, mild steel, stainless steel, or case hardened steel. Used to reduce the size of a bearing I.D. (Inner Diameter) to the size of the O.D. (Outer Diameter) of the Axle. Also known as a spanner bushing because it spans the gap inside the forks to add strength to the caster. Because its length is just a bit wider than the hub length of the wheel, it allows the forks to be tightened all the way onto the spanner instead of on the Hub of the wheel, which would interfere with wheel rotation. In addition, on Roller Bearings, bushings act as the inner raceway for the bearing roller to roll on. Most are cross-drilled to allow grease to be injected in through the Zerk axle, pass through the bushing, and reach the bearings.

Caster: An assembly of individual parts designed to allow a cart or piece of equipment to roll while under a load. Swivel Casters and Rigid Casters used together on the same cart allow the cart to be steered more easily whereas carts with all swivel casters allow the cart to turn within its own radius.

Delrin: Acetal (the generic name for a family of products) provides high strength and stiffness along with increased dimensional stability and ease of machining. Low moisture absorption, low coefficient of friction as well as good wear properties make Delrin ideally suited for close tolerance mechanical parts.

Expanding Adapters: A fastener design that uses a rubber adapter that expands as it is compressed between a knurled nut and a plastic base. Used primarily in the Food Service industry because it fits into the round legs of food processing tables. Can be used in either square or round tubing. Sold with all the parts as an Expanding Adapter Kit.

Fastener: The part of a caster that is used to attach the caster to the product it is used on. The most common fastener used and the strongest fastener type available is the Top Plate. Other styles are not as strong but are used when space does not allow for a top plate. Such as, Threaded Stem, Grip Ring Stem, Square Stem, Round Stem, Octagon Stem, and Expanding adapters.

Forks: Also known as the legs of a caster, the forks of a caster support the wheel and hold it in place as the caster is moving. There are two basic designs: Stamped or Cut and welded. Stamped forks are generally used on light to medium duty casters. Cut and welded forks are mainly used on medium to heavy duty casters.

Hub Length: The distance measured through the bore of the wheel from one side of the hub to the other. The hub length of a wheel should be less than the length of the spanner bushing in order for the wheel to function properly while it turns inside the fork legs. This measurement is critical when you are replacing the wheel only on a caster.

Inner Diameter (I.D.): The term used to refer to the inside measurement of an object: i.e. Wheel Bore, Bearing Bore, Bushing Bore etc.

Kingpin: The bolt or rivet that holds the swivel section of the Raceway together. This is the weakest point of the swivel caster and will usually fail first before any other part. The Swivel Offset causes pressure on the kingpin, which can stretch or shear the kingpin depending on the amount of Shock Load the kingpin is subjected to. Nut and bolt style kingpins are the strongest style and can be maintained by retightening the raceway if it starts to stretch. Rivet style kingpins are less expensive to manufacture but cannot be maintained.

Load Capacity: The maximum amount of weight a caster can hold and still function with optimum performance. This is not the failure capacity of the caster. However, any amount weight over the rated capacity will reduce performance and will eventually lead to premature failure. (See Key Measurements)

Overall Height: Overall height is the distance measured from top of the fastener to the bottom of the tread. This is the total height the caster raises the cart or piece of equipment off the floor. This is important information when replacing casters on a cart that are not from the same manufacturer. Also, critical when the cart must be rolled underneath another object and has to clear the object. (See Key Measurements)

Outer Diameter (O.D.): The term used to describe the outside measurement of an object: i.e. Axle, Bearings, Bushings etc.

Position Lock: Position locks have a spring-loaded rod that can be attached to a caster to stop the swivel from turning. The raceways are notched to accept the rod when engaged in 4 different 90-degree positions. Used when you want to convert a swivel caster to a rigid and back again as needed.

Quick Change Plate: Quick Change Plates are plates that can be bolted or welded to a cart, which allows a caster to be attached or removed without the use of tools. The caster top plate is inserted from the side and is held in place by a heavy-duty spring clip. These are very useful when casters are only needed temporarily or are changed often.

Raceway: A raceway is the set of bearings in the caster that assists the caster in swiveling while under a load. Can be used in a Single ball raceway or a Double ball raceway design. Double ball raceways are better between the two styles because the Upper raceway handles the majority of the load while the Lower raceway handles the majority of the thrust when swiveling. Single ball raceways must handle both on one set of bearings and are more likely to bind when under heavy loads. (The diagram shows the Upper on the bottom and the Lower on the top because this is a view of the caster in an inverted position.)
Rigid Casters: Rigid casters only allow bi-directional movement: forward or backward. Although the rigid is stronger and can take a higher load capacity, it is rated the same as the swivel for safety reasons. As an option the forks can be double welded to give added strength and help withstand Side Thrust prone applications.

Side Thrust: Side thrust occurs when a cart is hit or bumped by another object in a sideways motion and the swivel casters are not able to turn with the motion because of an obstruction. Affects on rigid casters can cause the forks to collapse and make the caster totally inoperable.

Swivel Casters: Swivel casters allow omni-directional movement and have either one or two sets of Raceways that allow a caster to swivel 360 degrees while under a load. Load capacity of each caster is based on the capacity of the swivel section.

Swivel Offset: The distance measured from the center of the kingpin to the trailing edge of the wheel. Important when the caster used in an enclosed area where the caster could be prevented from swiveling 360 degrees. (See Key Measurements)

Shock Load: The overloading of the kingpin due to the cart being moved mechanically over an obstruction: i.e. Curbs, tracks, thresholds, expansion joints, cracks, unclean floors etc. Also, can be due to the cart being picked up vertically and dropped while under a load: i.e. Dumpsters, trash bins, bulk part loaders etc. Can cause premature failure of the kingpin.

Tread Width: Tread width is measured laterally across the tread of the wheel. The larger the tread the more the weight can be spread out over a distance and allows higher capacities. Large widths can also increase the amount of friction with the floor and greatly increases the effort necessary to start the carts motion. (See Key Measurements)

Wheel Diameter: The distance measured from one side of the tread to the other. Important when you are replacing the wheel only on a caster. (See Key Measurements)

Zerk: A grease lubrication fitting that can be found on the raceway, axle, or hub of the wheel.