CAPACITY.  The maximum recommended load per caster or wheel based on intermittent operation over smooth floors at speeds not exceeding 3 mph, with no shock loading or adverse environmental conditions.

CASTER SIZE.  A term for classifying casters, based on the nominal diameter of the wheel.

COMPONENT THRUST.  Designates side forces exerted on a swivel caster and properly counteracted by the secondary load bearing.

DIRECT THRUST.  Designates downward forces exerted on a swivel caster and properly counteracted by the secondary load bearing.

DUROMETER.  A measure of the hardness of resilient tread wheels.

FACE.  The width of the wheel tread cross-section, measured at the base of the tread rather than at the point of floor contact.

HORN BASE.  The flat part at the top of the horn from which the legs extend.  Serves as a lower raceway for main load bearing, and may provide a seat or upper raceway for secondary load bearing.

KINGPIN.  A rivet, or threaded stud or bolt with nut, that holds the mounting plate and horn assembly of a swivel caster together.  Forged as an integral part of mounting plate on higher quality casters for maximum rigidity and strength.

KINGPINLESS. A new kind of caster that replaces its kingpin with a precision, full contact ball bearing raceway.

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.

LEGS.  Axle support brackets which extend down from the horn base of a swivel caster or the mounting plate of a rigid caster.

MAIN LOAD BEARING.  Steel balls or rollers that swivel the horn base in relation to the mounting plate of a rigid caster.

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

OVERALL HEIGHT.  The vertical distance from the top of the caster mounting plate to the bottom of the wheel.

RACEWAY.  A surface in which bearing balls or rollers rotate.

RETAINER WASHER.  A steel washer pressed into the hub ends of some roller bearing wheels to hold the bearing in place.

SECONDARY LOAD BEARING (COMMERCIAL).  The row of steel balls that rides in the raceway between the horn base and the secondary bearing retainer of a swivel caster to counteract component thrust.

SECONDARY LOAD BEARING (PRECISION).  A precision self-contained bearing, usually a tapered roller bearing, operating between the horn base and the kingpin of a swivel caster.  Constitutes the most efficient means of assisting swivel action by counteracting thrust.

RIG. A swivel or rigid caster assembly less wheel (may or may not include axle, nut, or spanner bushing).

ROLLABILITY. The ease of starting and rolling, measured by drawbar pull.  This is determined by load, floor conditions, wheel type and sizes, and bearings.

SPANNER BUSHING.  A non-rotating sleeve of seamless steel tubing that fits over the axle in many casters.  Serves the dual purpose of providing a smooth inner raceway for the wheel bearings, and strengthening the caster by permitting the legs to be tightened against it.

SWIVEL LEAD.  (also called 'offset') The perpindicular distance between the vertical centerlines of the kingpin and the axle of a swivel caster.  Larger offsets afford easier swiveling, shorter offsets greater strength.

SWIVEL RADIUS. The horizontal distance from the centerline of the caster kingpin to the outer edge of the wheel (a measure of clearance required to swivel a caster 360°).

THRUST WASHER. A steel washer between the hub ends of the wheel and the inside of the caster legs.

YOKE.  Alternate term for 'rig'.