Glossary of Caster Terms

Below is an alphabetical list of popular caster terms used throughout the industry.

AXLE NUT

Nut on the side of the rig fork that secures the thrust washers, spanner bushings, and bolt or lube axles together.

BOLT HOLE PATTERN

The bolt hole pattern is the horizontal and vertical measurement of distance between the center of one bolt hole to the opposite center of the other bolt hole.

BORE DIAMETER

Distance measured through the center of the wheel.

BRINELLING

Permanent deformity of a ball raceway caused by severe impact or shock load that exceeds the material limit on ball bearings.

CASTER/CASTOR

A pivoting roller attached to the bottom of furniture, trucks carts, portable machines, etc. to make them movable. Available in different sizes and materials. (Refer to the Caster Connection Rig Type Chart and Wheel Type Chart for more information.)

CASTER PAD

A mechanism used for quick replacement of a plate mounted caster. The caster slides into the caster pad and is secured using only one axle and nut.

COMMERCIAL/INDUSTRIAL BEARING

The row of steel balls that rides in the raceway between the fork base and secondary bearing retainer of a swivel caster to counteract component thrust. It is this bearing that characterizes the popular "double ball race" caster.

COMPONENT THRUST

Distributes side forces exerted on a swivel caster and appropriately offset by the secondary load bearing.

COTTER PIN

A small metal pin used to keep other parts from changing their arrangement and location.

DIRECT THRUST

Designates those downward forces exerted on a caster by the load weight, and offest by the main load bearing.

DUROMETER

Scale for measuring or measurement of the hardness of a wheel material.

DYNAMIC LOAD

Load that is imposed while caster or wheel is in motion.

HUB LENGTH

Hub length is the widest part of the hub (including bearing assembly and thread guards).

IMPACT LOAD

Load exerted on a caster/wheel by shock or vibration.

KINGPIN

A rivet or threaded stud or bolt with nut, which holds together the mounting plate and fork assembly of a swivel caster.

KINGPIN NUT

The nut on the bottom of a threaded kingpin or bolt that permits the disassembly or adjustment of swiveling components; a maintenance feature of better casters not found with rivet-type kingpins.

KINGPINLESS

A swivel section which is held together without a rivet or nut and bolt kingpin. Kingpinless swivel sections are held together by a single row of ball bearings which are contained by a full contact interlocking swivel raceway design.

RIG / FORK/ HORN / YOKE LEGS

Support brackets that extend downward from a swivel caster's fork base or the mounting plate of a rigid caster.

LOAD CAPACITY

The maximum amount of weight a caster or wheel will hold. The maximum recommended load per caster or wheel based on intermittent operation over smooth floors at speeds not exceeding 3 m.p.h., with no shock loading or adverse environmental conditions. Total load capacity per application can be calculated by taking the gross weight of a truck/dolly and dividing by three. This calculation assumes a four caster configuration is being used on the application.

LUBE BOLT AXLE

An axle containing a lubrication hole allowing for lubrication of the spanner bushing without disassembling the wheel from the fork legs.

LUBRICATION FITTING

A fitting place into higher quality casters that allows for lubrication of the bearings without disassembling the fork base, main, and load bearings.

MAIN LOAD BEARING

The row of steel balls or rollers that allow forks to swivel in relation to the mounting plate of a swivel caster, and offsets direct thrust.

MOUNTING PLATE

The flat base, usually with four bolt holes, that forms the top of a caster and permits attachment by bolting or welding to a flat surface.

OFFSET/SWIVEL LEAD

The perpendicular distance between the vertical centerlines of the kingpin and the axle of a swivel caster. Longer swivel leads create easier swiveling, but capacity is reduced with swivel lead length. Shorter swivel leads increase capacity and decrease swivel ability.

OVERALL HEIGHT

The total vertical distance from the floor to the top of the mounting plate/base of the caster stem.

PLATE DIMENSION

Measured distance from one edge of the top plate to its opposite side and the distance from the other edge of the top plate to its opposite side.

PLATE-MOUNT CASTER

Plate-mount casters use a plate to connect to a cart, shelving, or other project.

Plate-mount casters are much stronger than stem-mount casters and are normally the first option when you need a caster for heavy industrial settings. The “plate” in plate-mount casters is simply a flat piece of metal that uses bolts to attach to a cart. Because of this flat piece of metal, you have great stability and durability.

Plate-mount casters come in a few different dimensions that are worked into CAD drawing plans.

RACEWAY

The area of the rig in which ball bearings or rollers rotate, which allows a caster to swivel.

RETAINING WASHER

A washer pressed into the hub ends to hold bearings in place. Sealed retaining washers keep grease in and debris out of the bearings.

RIG / FORK / HORN /YOKE

The part of the caster that is made up of legs and a base (fork base on swivel caster or mounting plate on rigid). All of the pieces of a caster minus the wheel. Example: top plate, ball bearings, upper race, lower race, fork legs, rivet/kingpin, lock nut, axle.

RIG BASE

The flat part at the top of the rig from which the rig horns/legs extend. Provides lower raceway for main load bearing, and may provide an upper raceway for secondary load bearing.

ROLLABILITY

The ease of beginning and maintaining rolling motion as determined by factors including material/durometer of wheel, floor conditions/surfaces, load and size of wheel and the wheel bearings.

PRECISION BEARING

A self contained precision bearing, usually a tapered roller bearing, operating between the fork base and the kingpin of a swivel caster. Promotes the most efficient means of aiding swivel action by counteracting component thrust.

SPANNER BUSHING

A non-rotating steel tubing that fits over the axle in many casters. Provides a smooth inner raceway for wheel bearings, and strengthens the caster by allowing the legs to be tightened against it.

STANDARD/SOLID BOLT AXLE

An axle that attaches the wheel to the fork legs of a caster.

STATIC LOAD

Load that is imposed while caster or wheel is not in motion.

STEM

In alternative to a plate, an obtruded object (usually at the top center of a caster) that fits into the bottom of the leg or bottom of the object that the caster is carrying.

• A Comprehensive Review of Stem Casters

STEM SIZE

The length and diameter of a caster's stem.

SWIVEL LEAD

The distance between the centerline of the kingpin and the centerline of the axle of a swivel caster. The larger the offset the easier swiveling, but the smaller offset offers greater strength.

SWIVEL LOCK

A mechanism that attaches to the top plate of a swivel caster that when engaged locks the caster for only straight line movement.

SWIVEL RADIUS

The horizontal distance measurement from the center of the kingpin to the outside edge of the tread of the wheel.

STEM

The “stem” in stem-mount casters is an elongated piece of metal that inserts into a cart, fixture, etc. This means that there will need to be a hole of some sort that matches with your stem, and stems come in many different shapes, sizes, and configurations.

STEM-MOUNT CASTER

Stem-mount casters use a stem to connect to a cart, shelving, or other project. Stem-mount casters are in general not as strong as plate-mount casters, so for most industrial applications, you will not use stem-mount casters. Stem-mount casters are excellent for DIY projects, healthcare, hospitality, food processing, and quite a few other industries.

THRUST WASHER/RETAINING WASHER/COMBINATION SEAL

A steel washer between the hub ends of the wheel and the inside of the caster legs. A steel washer pressed into the hub ends of some roller bearing wheels to hold the bearing in place.

TOP PLATE

The “plate” in plate-mount casters is a flat piece of metal that uses bolts to attach to a cart.

TREAD WIDTH

Width of the outer surface wheel.

TREAD FACE

The outer surface of the wheel that comes into contact with the ground/floor.

WHEEL

A round device that is designed to bear weight and easily move objects by turning around an axle passed through the center of the structure. (For more information on caster wheel materials, sizes and treads, please refer to the Caster Connection Wheel Type Chart)

WHEEL DIAMETER

Measurement of a wheel from opposite sides.