Caster & Wheel Basics
Selecting the Proper Caster and Wheel
Many factors must be taken into consideration in order to select the proper industrial caster or wheel. To make the most appropriate selection for your application, consider the following:
- Load Weight – The heaver the load, the larger the wheel required for the caster. The weight of the load also influences wheel mobility. For heavy duty loads over 400 lbs., roller or ball bearings are recommended.
- Floor Conditions – Be sure the wheel selected is large enough to pass over cracks in the floor, tracks, molding, and other obstructions. Use polyurethane or Performa rubber wheels for floor protection on linoleum, tile, carpet, etc.
- Unusual Conditions – Each wheel material has characteristics which will provide the best results where unusual conditions exist. For example Polyurethane, polyolefin, phenolic, or steel wheels are recommended where acids, oils, chemicals, and other substances harmful to rubber are present.
- Rolling Ease – The larger the wheel, the easier it rolls. While roller bearing wheels can carry heavier loads, ball bearing wheels roll more easily but carry lighter loads. Whenever possible, use the largest ball bearing wheel necessary for best results.
- Extreme Climates – Room temperatures are not a problem for most casters. However extreme cold and heat can be a problem. Bastian casters come standard with lubrication designed to withstand temperatures from 450°F below zero to 2600°F above zero.
- Shock Load – The impact caused by dropping a load on a cart or truck, or by rolling on a rough surface. When encountering shock loading, you will need to look at four things: construction of the caster, type of kingpin, swivel bearing, and the composition of the wheel.
Caster Parts Definitions & Nomenclature
| Caster/Castor A pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable. |
Fork/Horn/Yoke The caster part which is comprised of legs plus a base (fork base of swivel caster or mounting plate of rigid). |
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| Wheel A round structure, solid disk or a rigid circular ring, that is designed to turn around a center, normallly 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 synomous with the material makeup or specalized tred pattern exhibited by the wheel. |
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. |
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| Rig A swivel or rigid caster assembly less wheel, that may or may not include axle, nut or spanner bushing. |
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. |
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| 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. |
Legs The axle-support brackets extending down from the fork base of a swivel caster, or from the mounting plate of a rigid caster. |
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| 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 |
Standard/ Solid Bolt Axle An axle used to attach the wheel to the fork legs of a caster. |
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| 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. |
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 whout disassembing the wheel from the fork legs. |
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| 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. |
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| 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. |
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. |
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| 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. |
Axel Nut The nut on the side of the leg that holds the thrust washers, spanner bushings, and bolt or lube axles together. |
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| 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 |
Raceway A surface in which bearing balls or rollers rotate. |
Caster Parts Dimentional Definitions & Nomenclature
| Wheel Diameter Wheel diameter is the outer nominal diameter of the wheel. |
Bolt Hole Spacing Bolt hole spacing is the distance measured from the center of the bolt hole to the opposite center of the other bolt hole. |
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| 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). |
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| 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). |
Bore Diameter Bore diameter is the distance measured through the center of the wheel |
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| 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. |
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. |
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| Capacity The maximum recommended lad per caster or wheel based on intermittent operation over smooth foloors 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 |
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. |
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| 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. |
Swivel Lead Swivel lead is the horizontal distance between vertical centerlines through kingpin and wheel center. |
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Caster Measurement Definitions & Nomenclature
| Durometer A measure of the hardness of resilient tread wheels. |
Component Thrust Designates side forces exerted on a swivel caster and properly counteracted by the secondary load bearing. |
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| 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. |
Direct Thrust Designates those downward forces exerted on a caster by the load, and counteracted by the main load bearing. |
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- Ridgid
A rigid Caster has a rigid yoke and wheel assembly which permits only straight-line movement. - Swivel
A swivel caster has a swivel yoke and wheel assembly that will allow rotation of 360 degrees, which permits movement in any direction. - Locking
A locking caster is an assembly that can be locked in place by some sort of mechanic device.
Caster Types
