Caster Terminology and Wheel Glossary
Caster Terminology & Wheel Glossary
Understanding caster and wheel terminology makes it easier to choose the right product for your equipment, floor conditions, load requirements, and operating environment. Use this glossary to learn common caster parts, wheel materials, mounting styles, measurements, bearings, brakes, and performance terms.
Whether you’re replacing an existing caster or designing new equipment, knowing these terms can help you compare products more accurately and select a caster or wheel that fits your application.
Caster Types & Mounting
Caster
A complete mobility assembly consisting of a wheel, axle, and caster rig or yoke. Casters mount to carts, racks, machinery, equipment, furniture, and other products to allow them to move.
Swivel Caster
A caster designed to rotate around a vertical swivel axis, typically allowing 360-degree movement. Swivel casters provide maneuverability and make it easier to change direction.
Rigid Caster
A caster with a fixed wheel orientation that rolls forward and backward but does not swivel. Rigid casters improve straight-line tracking and are commonly paired with swivel casters.
Plate Caster / Top Plate Caster
A caster mounted using a flat plate with bolt holes or slots. Plate casters offer a large mounting surface and are commonly used on industrial carts, machinery, platform trucks, and heavy equipment.
Stem Caster
A caster mounted using a stem rather than a top plate. Stem casters are often used on shelving, worktables, institutional equipment, furniture, and lighter mobile equipment.
Threaded Stem Caster
A stem caster with external threads that screw into a threaded socket, insert, nut, or mounting point.
Grip Ring Stem Caster
A caster with a smooth stem and retaining ring that compresses during installation and expands inside the socket to hold the caster in place.
Expansion Stem Caster
A stem caster that uses an expanding adapter inside square or round tubing. Tightening the assembly expands the adapter and secures the caster inside the equipment leg.
Hollow Kingpin Caster
A swivel caster containing a hollow center rivet or kingpin that can accept mounting hardware, bolts, or certain modular stem configurations.
Modular Stem Caster
A caster designed to accept interchangeable stems or mounting hardware, allowing one caster design to fit several mounting requirements.
Leveling Caster
A caster that combines mobility with an adjustable Leveling Caster. The equipment can be rolled into position and then stabilized by lowering the leveling foot.
Spring-Loaded Caster
A caster incorporating a spring mechanism that helps absorb shock, maintain wheel contact, or reduce vibration when equipment travels over uneven surfaces.
Low-Profile Caster
A caster designed to provide load capacity while keeping the overall mounting height as low as possible.
Dual-Wheel Caster
A caster containing two wheels mounted side by side. Dual-wheel designs can increase load capacity while improving maneuverability by allowing the wheels to rotate at slightly different speeds while turning.
V-Groove Caster
A caster equipped with a V-groove wheel designed to travel along angle iron, inverted track, or other compatible guide systems.
Flanged Caster
A caster or wheel incorporating one or more flanges that help guide the wheel along a rail or track.
Caster Measurements
Wheel Diameter
The outside diameter of the wheel measured across its center from one tread surface to the opposite tread surface. Larger wheels generally roll over floor joints, debris, and obstacles more easily than smaller wheels.
Tread Width
The width of the wheel surface that contacts the floor. Tread width can influence load distribution, rolling resistance, stability, and floor loading.
Overall Height / Mounting Height
The vertical distance from the floor to the top mounting surface of a caster. This measurement is important when replacing casters or maintaining a specific equipment height.
Swivel Radius
The horizontal distance from the center of the caster’s swivel axis to the outermost point of the wheel or brake as the caster rotates. Swivel radius determines the clearance required for unrestricted rotation.
Swivel Lead
The distance between the centerline of the swivel section and the centerline of the wheel axle. Swivel lead affects steering response, maneuverability, and swivel performance.
Bolt Hole Pattern
The center-to-center spacing of the mounting holes or slots in a caster top plate. Bolt hole patterns are normally specified by length and width.
Top Plate Size
The overall length and width of the caster’s mounting plate.
Mounting Bolt / Attaching Bolt
The bolt or fastener used to secure a caster to equipment. Bolt size must match the caster’s mounting holes and the requirements of the equipment being supported.
Hub Length
The overall distance from one side of a wheel hub to the other. Correct hub length is important for proper fit between caster legs or on an axle.
Bore
The opening through the center of a wheel or bearing where the axle, bushing, or bearing is installed.
Inner Diameter / I.D.
The inside diameter of a wheel bore, bearing, tube, or other circular opening.
Outer Diameter / O.D.
The outside diameter of a wheel, bearing, tube, socket, or other round component.
Load Capacity / Load Rating
The recommended maximum load a caster or wheel is designed to carry under specified operating conditions. Actual performance can be affected by speed, floor conditions, temperature, shock loading, and application environment.
Dynamic Load
The load applied to a caster or wheel while the equipment is moving.
Static Load
The load applied to a caster or wheel while the equipment remains stationary.
Caster Components
Axle
The shaft, bolt, or rivet that passes through the wheel and secures it between the caster legs.
Yoke / Fork / Rig / Horn
The structural portion of a caster that holds the wheel and connects it to the caster’s mounting or swivel assembly.
Stamped Yoke
A caster yoke formed from stamped steel rather than fabricated from several separately welded components.
Cut-and-Welded Design
A heavy-duty caster construction method in which components are individually formed and welded together rather than being produced from a single stamped piece.
Kingpin
The central bolt, rivet, or forged component that holds the swivel section of many traditional swivel casters together.
Kingpinless Caster
A heavy-duty swivel caster designed without a conventional center kingpin. The swivel load is distributed through the raceway and ball bearings, making kingpinless casters well suited for demanding industrial and shock-load applications.
Raceway
The circular track inside a swivel caster in which ball bearings rotate, allowing the caster to swivel under load.
Double Ball Raceway
A swivel assembly containing two rows or sets of ball bearings. The design helps support vertical loads while managing forces created during swiveling.
Dust Cap / Dust Cover
A protective cover used to reduce contamination from dirt, dust, fibers, and other debris entering a caster raceway or bearing area.
Retainer Washer
A washer used to retain bearings, bushings, grease, or other wheel components in their correct position.
Thrust Washer
A washer positioned between moving components, commonly between the wheel hub and caster leg, to reduce rubbing and control side movement.
Thread Guard
A disk or shield positioned beside a wheel to help prevent string, thread, wire, hair, and other debris from wrapping around the axle.
Seal
A protective component used around bearings or raceways to retain lubricant and help prevent contaminants from entering.
Zerk / Grease Fitting
A fitting that allows grease to be injected into a caster raceway, axle, or wheel bearing during maintenance.
Rivet Axle
A permanently installed axle commonly found on light-duty casters where routine wheel removal is not required.
Rivet Kingpin
A kingpin secured by forming or staking the ends of the rivet instead of using a removable nut and bolt.
Caster Pad / Weld Plate
A mounting plate welded or bolted to equipment to provide a secure surface for attaching a plate caster. Caster pads can also reinforce the mounting area or simplify caster replacement.
Quick-Change Plate
A mounting system designed to make caster installation and removal faster. Depending on the design, the caster may slide, bolt, or lock into the mounting plate.
Brakes, Locks & Accessories
Caster Brake
A mechanism that restricts wheel movement, caster swiveling, or both. Brake designs vary depending on caster style and application.
Brake Kit
A collection of components used to add or replace a caster brake. A kit may include the brake lever, pedal, mounting hardware, axle components, or other required parts.
Wheel Brake
A brake that prevents or restricts the wheel from rotating while generally allowing the caster swivel section to remain free.
Side Lock Brake
A wheel brake mounted beside the caster wheel and typically operated by foot.
Top Lock Brake
A braking mechanism that applies pressure to the top surface of the wheel tread to prevent the wheel from rolling.
Total Lock Brake
A brake that locks both the wheel and the caster’s swivel action. Total lock casters help keep mobile equipment stationary when the brake is engaged.
Directional Lock
A mechanism that locks the caster’s swivel section in a predetermined direction while allowing the wheel to continue rolling. Directional locks can make long carts easier to steer and track.
Swivel Lock
A device that prevents the caster from swiveling, effectively allowing a swivel caster to operate temporarily like a rigid caster.
Floor Lock
A floor-contacting accessory mounted beneath mobile equipment. When engaged, the floor lock helps stabilize the cart and reduce unwanted movement while the casters remain installed.
Wheel & Bearing Terms
Wheel
The rolling component itself, without the caster frame or mounting assembly.
Blank Wheel
A wheel supplied without a bearing installed, typically with a plain or unfinished bore.
Complete Wheel
A wheel supplied with its required bearing or bearing assembly installed.
Wheel Hub
The center section of a wheel surrounding the bore and bearing area.
Centered Hub
A wheel hub with approximately equal projection or dimensions on both sides of the wheel.
Offset Hub
A wheel hub that projects farther from one side of the wheel than the other. Offset hubs are common on hand trucks and other equipment using wheels mounted directly to an axle.
Wheel Core
The structural center of a wheel that supports the tread. Cores may be made from materials such as cast iron, aluminum, steel, nylon, or polyolefin.
Wheel Tread
The outer portion of the wheel that contacts the floor. Tread material and shape greatly influence noise, floor protection, rolling resistance, traction, and durability.
Crown Tread / Crowned Tread
A wheel tread with a slightly rounded profile. Reducing the size of the contact patch can make a wheel easier to turn and maneuver.
Plain Bore
A wheel that rotates directly on the axle or a simple bushing rather than using a conventional roller or ball bearing.
Bearing
A component inside the wheel hub that reduces friction between the wheel and axle, improving rolling performance.
Ball Bearing
A bearing containing steel balls that reduce friction between rotating components.
Precision Ball Bearing
A machined ball bearing designed for smooth, low-friction rotation. Precision bearings are often used when easier rolling, higher speeds, or frequent movement is required.
Sealed Precision Bearing
A precision ball bearing with seals or shields that help retain lubricant and protect the internal bearing surfaces from contamination.
Roller Bearing
A wheel bearing containing cylindrical rollers. Roller bearings are widely used in industrial caster wheels because they offer good load capacity and dependable rolling performance.
Tapered Roller Bearing
A heavy-duty bearing using tapered rollers to handle both radial and thrust forces. These bearings are frequently used in demanding or towed applications.
Sleeve Bearing / Bushing
A simple cylindrical bearing surface installed between the wheel and axle. Sleeve bearings can provide a durable, economical option for specific environments and loads.
Delrin Bearing
A low-friction engineered plastic bearing or bushing that offers corrosion resistance and can perform well in wet or washdown environments.
Bearing Cap
A protective or retaining component installed around certain wheel bearings to help position the bearing and reduce contamination.
Spanner Bushing
A tubular spacer positioned through a wheel bearing or hub. The axle passes through the spanner bushing, allowing the axle hardware to be tightened without compressing the wheel or bearing assembly.
Wheel Materials
Polyurethane Wheel
A caster wheel made with polyurethane tread or solid polyurethane construction. Polyurethane wheels are popular because they combine good load capacity, durability, floor protection, and relatively low rolling resistance.
Polyurethane on Cast Iron Wheel
A wheel with polyurethane tread bonded to a cast iron core. This construction combines a resilient floor-friendly tread with a strong core for industrial load applications.
Polyurethane on Aluminum Wheel
A wheel with polyurethane tread bonded to an aluminum core. Aluminum reduces wheel weight while maintaining strength and is commonly used in ergonomic and heavy-duty wheel designs.
Rubber Wheel
A wheel using rubber as the primary tread material. Rubber wheels generally provide a cushioned, quiet ride and good floor protection.
Mold-on-Rubber Wheel
A wheel made by molding and bonding rubber tread directly onto a rigid wheel core. Mold-on-rubber wheels provide cushioning, traction, noise reduction, and floor protection for many industrial applications.
High Modulus Rubber Wheel
A resilient rubber wheel designed for increased strength and load capability while maintaining a cushioned ride. Many high-modulus wheels use a rounded or donut-style tread to improve maneuverability and shock absorption.
Thermoplastic Rubber / TPR Wheel
A wheel made from a thermoplastic rubber compound. TPR wheels are known for quiet operation, floor protection, cushioning, and resistance to many common chemicals and cleaning solutions.
Phenolic Wheel
A hard industrial wheel made from phenolic resin combined with reinforcing materials. Phenolic wheels offer an economical combination of high load capacity, low rolling resistance, and resistance to many oils and chemicals.
Nylon Wheel
A hard thermoplastic wheel known for high load capacity, low rolling resistance, moisture resistance, and good resistance to many chemicals.
Polyolefin Wheel
A lightweight molded thermoplastic wheel resistant to water and many chemicals. Polyolefin wheels are commonly used in food service, institutional, material handling, and washdown applications.
Polypropylene Wheel
A thermoplastic wheel offering moisture and chemical resistance with a lightweight construction. Polypropylene is often used where easy cleaning and corrosion resistance are important.
Cast Iron Wheel
A solid metal wheel offering excellent load capacity and low rolling resistance on smooth industrial floors. Cast iron wheels are durable but provide limited floor protection and cushioning.
Forged Steel Wheel
A heavy-duty steel wheel manufactured through a forging process. Forged steel wheels are designed for exceptionally high loads, severe service, and demanding industrial environments.
Pneumatic Wheel
A wheel containing an air-filled tire. Pneumatic wheels provide excellent cushioning, shock absorption, and performance over rough or uneven surfaces.
No-Flat / Flat-Free Wheel
A pneumatic-style wheel designed to provide cushioning without requiring air pressure. No-flat wheels eliminate downtime caused by punctures or air loss.
High-Temperature Wheel
A wheel manufactured from materials selected to withstand elevated operating temperatures. Temperature limits vary by wheel material, bearing type, exposure time, load, and operating environment.
V-Groove Wheel
A wheel containing a V-shaped groove designed to follow angle iron or compatible track systems. Many V-groove wheels can also roll directly on a flat floor.
Flanged Wheel
A wheel containing a raised flange that helps keep the wheel aligned on rails or tracks.
Anti-Static Wheel
A wheel formulated to help reduce the accumulation of static electricity as equipment moves.
ESD / Static-Dissipative Wheel
A wheel engineered to dissipate electrostatic charge through a controlled electrical resistance range. ESD wheels are commonly used around sensitive electronics or equipment where static control is important.
Conductive Wheel
A wheel designed to provide an electrically conductive path between mobile equipment and the floor, helping discharge static electricity.
Manufacturing & Construction Terms
Chemical Bond
A bonding method that uses adhesives or chemical interaction to secure a wheel tread to its core.
Mechanical Bond
A tread-to-core attachment method that uses physical interlocking features in addition to or instead of chemical adhesion.
Cold Forged
A manufacturing process that forms metal under high pressure without heating it to conventional hot-forging temperatures. Cold forging can improve dimensional consistency, surface finish, and material strength.
Drop Forged / Hot Forged
A manufacturing process in which heated metal is formed under high pressure between dies. Forged caster components are commonly used where strength, durability, and resistance to impact are important.
Integrally Forged
A construction method in which multiple functional features are forged into a single component rather than being assembled from several welded pieces.
Keyway
A machined slot in a wheel bore designed to accept a matching key on a drive shaft. The key transfers torque from the shaft to the wheel.
Caster Performance Terms
Rollability
How easily a caster or wheel begins and continues rolling. Wheel diameter, tread material, bearing type, load, and floor condition all influence rollability.
Rolling Resistance
The force required to keep a loaded wheel moving across a surface. Lower rolling resistance generally means less effort is needed to push or pull equipment.
Starting Resistance
The amount of force required to begin moving equipment from a stationary position.
Swivel Resistance
The amount of force required to change the direction of a swivel caster.
Mobility
The overall ability of equipment to move and maneuver. Mobility is influenced by caster configuration, wheel material, wheel diameter, bearings, swivel lead, load, and floor conditions.
Ergonomic Caster / Ergonomic Wheel
A caster or wheel designed to reduce the force required to start, push, pull, turn, or maneuver equipment. Ergonomic performance can help reduce operator effort in frequently moved applications.
Durability
The ability of a caster or wheel to maintain performance while exposed to repeated use, loads, impacts, environmental conditions, and normal wear.
Durometer
A measurement of material hardness commonly used for rubber and polyurethane wheel treads. Shore A is commonly used for softer elastomers, while Shore D is typically used for harder materials.
Flat Spot
A flattened area that develops on a wheel tread after remaining loaded for an extended period or after material deformation. Flat spotting can cause vibration and an uneven ride.
Shock Load
A sudden impact force placed on a caster or wheel, such as dropping material onto a cart or striking floor joints, thresholds, or obstacles.
Side Thrust
A horizontal force applied sideways to a caster rather than in its normal rolling direction. Excessive side thrust can place additional stress on swivel components, axles, and mounting hardware.
Floor Protection
The ability of a wheel to minimize scratching, chipping, denting, or other damage to the floor surface.
Non-Marking Wheel
A wheel made from material formulated to reduce visible marks or streaks on flooring during normal use.
Shock Absorption
A wheel or caster’s ability to cushion impacts and vibrations as equipment travels across rough floors, joints, thresholds, or debris.
Continuous Temperature Rating
The temperature range in which a caster or wheel is designed to operate for sustained periods under the manufacturer’s specified conditions.
Intermittent Temperature Rating
A higher or different temperature limit permitted for short-duration exposure rather than continuous operation.
Autoclavable Caster / Wheel
A caster or wheel manufactured from materials capable of tolerating specified autoclave sterilization conditions involving heat, steam, pressure, or repeated cleaning cycles. Always verify the manufacturer’s temperature and exposure limits.
Industry Terms
MRO
Maintenance, Repair, and Operations. MRO products are used to maintain facilities, machinery, production equipment, and other business operations.
OEM
Original Equipment Manufacturer. OEM casters and wheels are selected or designed for installation on equipment during manufacturing.
NSF
NSF is an independent organization that develops public-health standards and provides product testing and certification. Certain caster products may be NSF certified or listed for applications such as food service and commercial equipment.
Washdown Application
An environment where equipment is regularly exposed to water, cleaning chemicals, detergents, or sanitation procedures. Stainless steel, polymer, sealed-bearing, and corrosion-resistant caster designs are often selected for these applications.
Corrosion-Resistant Caster
A caster manufactured with materials or finishes selected to resist rust and corrosion in wet, humid, chemical, food-processing, pharmaceutical, or washdown environments.
Heavy-Duty Caster
A caster engineered for higher loads or demanding industrial service. Heavy-duty designs may incorporate thicker steel, forged components, larger bearings, stronger raceways, and wider wheels.
Kingpinless Heavy-Duty Caster
A heavy-duty swivel caster that eliminates the traditional center kingpin and distributes swivel forces through a large raceway. This construction is frequently selected for shock loads, towing, manufacturing, aerospace, automotive, and other demanding applications.