Caster Jargon

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Caster Parts Definitions & Nomenclature:
Axel Nut
The nut on the side of the leg that holds the thrust washers, spanner bushings, and bolt or lube axles together.
Caster/Castor
A pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable.
Cotter Pin
A small metal pin used to keep other parts from changing their position, such as to keep a nut from turning, fastened in place by spreading apart its ends after it is inserted
Fork Base
The flat part at the top of the fork from which the legs extend. Serves as lower raceway for main load bearing, and may provide a seat or upper raceway for secondary load bearing.
Fork/Horn/Yoke
The caster part which is comprised of legs plus a base (fork base of swivel caster or mounting plate of rigid).
Kingpin
A rivet, or threaded stud or bolt with nut, that holds the mounting plate and fork assembly of a swivel caster together. Forged as an integral part of mounting plate on higher quality casters
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
The axle-support brackets extending down from the fork base of a swivel caster, or from the mounting plate of a rigid caster.
Lube Bolt Axle
An axle used to attach the wheel to the fork legs of a caster, 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 swivels the fork base in relation to the mounting plate of a swivel caster, and counteracts direct thrust.
Mounting Plate/Top 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.
Raceway
A surface in which bearing balls or rollers rotate.
Rig A swivel or rigid caster assembly less wheel, that may or may not include axle, nut or spanner bushing.
Secondary Load 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.
Secondary Load Precision Bearing
A precision self contained bearing, usually a tapered roller bearing, operating between the fork base and the kingpin of a swivel caster. Constitutes the most efficient means of assisting swivel action by counteracting component thrust.
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.
Standard/ Solid Bolt Axle
An axle used to attach the wheel to the fork legs of a caster.
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.
Wheel
A round structure, solid disk or a rigid circular ring, that is designed to turn around a center, normally an axle passed through the center of the structure. Caster wheels come in a wide variety of materials, sizes and treads. Often Caster wheel type is synonymous with the material makeup or specialized tread pattern exhibited by the wheel.
Caster Parts Dimensional Definitions & Nomenclature:
Bolt Hole Pattern/Spacing
Bolt hole spacing or the pattern is the distance measured from the center of the bolt hole to the opposite center of the other bolt hole.
Bore Diameter
Bore diameter is the distance measured through the center of the wheel.
Capacity
The maximum recommended lad 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. *Gross weight of a truck or dolly should be divided by the number of casters or wheels on which the weight is distributed.
Caster Size
A loose term for classifying casters, based on the nominal diameter of the wheel. For example, a “6 inch caster” is any caster having a 6 inch diameter wheel.
Hub Length
Hub length is the widest part of the hub (including bearing assembly and thread guards).
Offset/Swivel Lead
The perpendicular distance between the vertical centerlines of the kingpin and the axle of a swivel caster. Larger offsets afford easier swiveling, shorter offsets greater strength.
Overall Height
Overall height is the vertical distance between floor and mounting plate. (NOTE: Casters with threaded stems are measured to the top washer and do not include the length of the threaded stem).
Plate Dimension
Plate dimension is the measured distance from one edge of the top plate to the opposite side and the distance from the other edge of the top plate to the opposite side.
Swivel Lead
Swivel lead is the horizontal distance between vertical centerlines through kingpin and wheel center.
Swivel Radius
A swivel radius is the horizontal distance from vertical centerline of kingpin to outside edge of wheel tread. Specifies minimum clearance required for mounted caster to swivel 360 degrees.
Tread Width/Face
The outer surface of the wheel, in contact with the ground. The width of the wheel tread cross-section, measured at the base of the tread rather than at the point of floor contact.
Wheel Diameter
Wheel diameter is the outer nominal diameter of the wheel.
Caster Measurement Definitions & Nomenclature:
Component Thrust
Designates side forces exerted on a swivel caster and properly counteracted by the secondary load bearing.
Direct Thrust
Designates those downward forces exerted on a caster by the load, and counteracted by the main load bearing.
Durometer
A measure of the hardness of resilient tread wheels.
Rollability
Ease of starting and rolling, measured by drawbar pull. This is determined by load, floor conditions, and type and size of wheels and bearings.
Information sourced from the Colson Group USA.

 

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