1. Caster Terminology
   

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Capacity  The maximum recommended load per caster or wheel. Capacity is based on intermittent duty over smooth surfaces at speeds not exceeding 3 MPH; no shock loads or adverse environment conditions.

Caster Size  A method of classifying casters based on the nominal diameter of the wheel.

Component Thrust  The side forces exerted on a swivel caster by the load, counteracted by the Secondary Load Bearing.

Direct Thrust The download forces exerted on a caster by the load, counteracted by the Main load Bearing.

Drawbar Pull  The pulling force required to move a wheel under rated load.

Durometer  The measurement of the hardness of rubber or other tread and core materials.

Dynamic Load  The load imposed upon a caster or wheel while in motion.

Horn  The part of the caster that comprises legs plus the horn base of a swivel caster or the mounting plate of a rigid caster.

Horn Base  The flat part at the top of the horn which the legs extend from. This serves as the lower raceway for the Main Load Bearing and may provide the upper raceway for the Secondary Load Bearing.

Hub Length The width of the wheel at the hub. Hub length with combination retainer/thrust washers, add 3/16” to length.

King Pin  A rivet, stem stud or bolt with nut used to hold the mounting plate and horn assembly of a swivel caster together.

King Pin Nut  The nut on the bottom of a threaded king pin or bolt that permits the disassembly or adjustment of the swiveling components.

Legs The axle support brackets extending down from the horn base of a swivel caster or the mounting plate of a rigid caster.

Main Load Bearing  The row of steel ball bearings or rollers that swivels the horn base in relationship to the mounting plate and counteracts direct thrust.

Mounting Plate  The flat base, usually with 4 mounting holes that form the top of the caster. This permits attachment by bolting or welding to the equipment.

Offset  The distance from the center of the king pin to the center of the axle. Also called the swivel lead.

Overall Height The distance from the floor to the top of the mounting plate.

Raceway  A surface in which bearing elements rotate.

Retaining Washer  A steel or plastic washer pressed into the hub ends to hold the bearing in place.

Rig  A swivel or rigid caster assembly less the wheel, axle, nut and spanner bushing.

Rollability  The ease which a wheel or caster can be rolled. It is effected by load, floor conditions, wheel material, diameter of the wheel and type of bearing. It is measure by drawbar pull.

Secondary Load Bearing  A row of steel ball bearings or a tapered roller bearing that operates between the horn base and secondary bearing retainer or king pin to counteract component thrust.

Shock Load  The momentary load imposed upon a caster or wheel when a load is dropped or the equipment strikes an obstruction or experiences vibration.

Spanner Bushing  A steel or plastic sleeve that fits over the axle serving a dual purpose of providing a smoother inner raceway for the wheel bearing and to strengthen the caster by allowing the legs to be tightened against it.

Static Load  The load imposed upon a caster when it is stationary.

Swivel Radius  The distance from the center of the king pin and the outside edge of the wheel.

Temperature Range  The operating temperature range of the wheel material at rated loads.

Thrust Washer  A steel or plastic washer between the wheel hub and the inside of the caster leg.

Tread Width  The width of the wheel tread cross-section at the tread base.

Yoke  Another term for the horn.