Medium-Duty Casters (100–500 kg per Caster): Applications and Specifications to Fix Before the RFQ

Set the load rating basis per caster first

The rating you write into the RFQ is not the static share of the cart's weight. Once the cart rolls, dynamic forces rise above the parked figure, and shock events such as curbs, dock plates and potholes add impact that a static calculation never sees 9 18 .

That is why the rating has to be set above the static share before any other choice is made. Sources give two ways to get there.

One divides the total loaded cart weight by 3 — the 3-corner rule, on the assumption that one caster may be airborne — and adds a 20% safety factor 1 .

The other adds a 10–20% safety buffer to the total load and then divides by the number of casters, uprating again if loads shift during motion 9 . Both then round up to the nearest standard rating 19 .

Worked instance from the 3-corner method: a 3,000 lb cart needs four casters rated about 1,200 lb each, not 750 lb each 1 . The two methods do not produce the same number, so pick one basis, record it on the RFQ, and require every quote to be priced against it.

Two conditions change the basis again. Frequent movement over rough floors with thresholds or joints raises impact loads and calls for uprating plus larger-diameter or wider-tread wheels 9 18 .

Continuous 24/7 operation is a derating condition rather than an uprating one: one vendor-tier source advises reducing capacity by 25–33% because published ratings describe intermittent service 33 . That figure is a single source's guidance, not a standard, so treat it as a question to put to the supplier rather than a rule.

Pick the wheel material and tread for the application

Material hardness and elasticity drive floor protection, noise and chemical resistance, so the application selects the material rather than the other way round 2 20 22 .

Polyurethane is the common general-purpose industrial choice: it combines the hardness of plastic with the elasticity of rubber, giving load capacity, abrasion resistance and chemical resistance, and it resists cracking and surface damage in continuous operation 2 10 .

Rubber is the choice where shock absorption, vibration dampening and quiet rolling matter most, and it is common on healthcare, retail and food-service carts 2 21 . In AGV work the split is sharper.

One AGV-focused comparison rates polyurethane good on shock, wear, floor protection and noise, and rates standard nylon poor on shock, wear and floor protection with high noise 20 . That is a comparison for that application, not a general rule about nylon.

One supplier's order history illustrates the pattern rather than setting a market share: roughly 70% of the wheel SKUs that supplier ships weekly are polyurethane, and its rubber wheels ship most often to healthcare OEMs, furniture makers and food-service carts 2 . Use it as a directional signal only.

No source in this set gives a durometer or hardness value that is mandatory for 100–500 kg casters; the hardness figures cited elsewhere are product-specific. If hardness matters to your floor or your noise target, make it an RFQ question rather than a specification you assume.

Match the mounting plate and bolt pattern to the frame

Plate mounting is the most common industrial configuration, and it is where most measurement errors happen. Plate size, bolt-hole spacing and hole diameter must match the equipment frame, and the mounting pattern has to be confirmed before the order is placed 25 27 .

Measure center-to-center, not edge-to-edge, and measure both the short and the long spacing; a tape measure can introduce 1–2 mm of error, which is enough to cause a fitment problem 25 . A common medium-duty plate is 75×100 mm with a 55×75 mm bolt pattern 25 .

• ✓Measure plate length × width and compare with the frame's mounting surface
• ✓Measure bolt-hole center-to-center spacing in both directions
• ✓Measure bolt-hole diameter and check bolt clearance
• ✓Confirm the mounting pattern with the supplier before ordering
• ✓Check required load height against the existing equipment height

Choose wheel diameter and overall height together

Diameter sets push effort and obstacle rollover, and height sets whether the cart still fits its rack and work surfaces. Larger wheels roll more easily and handle obstacles better, and they distribute weight more effectively, which helps caster life 18 .

The push-force effect is measurable: each 1 inch of additional wheel diameter is stated to drop push force by about 10–15% 4 . Diameter also has a common starting point for this class.

A 100 mm (4 in) wheel is listed as the standard size for industrial carts and medium equipment, with 125 mm (5 in) for heavy-duty carts and scaffolding 26 . Height is the constraint that often decides the choice.

Replacement casters must match the overall height of the originals, or the equipment sits unlevel; a 5 mm height difference across four casters can cause noticeable rocking 25 .

Overall height is approximately wheel radius plus fork-to-axle offset plus plate or stem height, but the practical instruction is to measure it directly and use the formula only when specifying a custom caster 25 .

Select the bearing type for the duty cycle

The bearing is the part that rotates around the axle, and a caster that is otherwise well specified will still fail if the bearing cannot take the duty cycle 6 . Bearing choice should follow load, speed, movement frequency, contamination risk and maintenance access 31 .

Plain bearings are simple, economical and tolerant of rugged use, but rolling effort rises as load or movement frequency increases 31 . Roller bearings carry load well and handle shock, and are described as the default for heavy-duty work, but they need lubrication and protection from dirt and moisture 31 33 .

Precision sealed ball bearings give the lowest rolling resistance and suit long runs and powered equipment such as AGVs 6 33 . The push-force difference is stated as 30–40% when upgrading from plain to precision ball bearings 4 .

One supplier publishes load ranges by bearing family — plain up to 1,200 lb, annular ball up to 1,500 lb, precision sealed up to 2,200 lb, roller up to 3,500 lb per wheel 6 .

Those are that supplier's figures and do not establish a standard bearing capacity for this caster class, so use them as context rather than a selection rule. Maintenance follows from the bearing.

One vendor-tier source advises re-greasing every 3–6 months under normal use and monthly under heavy duty, and inspecting for flat spots and kingpin looseness 33 . That interval is one source's guidance, not a standard; ask the supplier what interval their bearing actually requires.

Set frame finish, sealing and wheel material for the environment

Washdown, disinfectant and cleanroom exposure change the frame, the bearing and the wheel together. A caster described as compliant for pharmaceutical cleanrooms uses a 304 or 316L stainless steel frame, non-shedding wheels, sealed bearings and a crevice-free, easy-to-clean design 28 .

Where disinfectants and washdowns are present, 316L is preferred over 304 for corrosion resistance; 304 is described as suitable for drier support areas 28 . Double-sealed stainless steel ball bearings are the preferred bearing for pharmaceutical casters because they prevent grease leakage and reduce contamination risk 28 .

Cleanroom class narrows the choice further. ISO 7 areas typically require sealed bearings and non-shedding wheel materials, while ISO 8 areas generally allow more flexibility 28 .

Where equipment moves between zones, the stricter of the two classifications applies 28 . Temperature is a separate check, and it is product-specific rather than class-wide.

One wheel product is rated -45°F to 200°F 5 , and two catalog caster items are rated -20°F to 180°F 3 . No source establishes a single washdown, steam or cleanroom class requirement that applies to all 100–500 kg casters, so confirm the temperature range and the cleaning chemicals against the specific product before ordering.

Specify the brake and swivel configuration

The swivel mix decides how the cart tracks.

Two swivel plus two rigid casters is recommended for most industrial carts because it tracks straight, is easier to control at speed and gives longer service life; four swivel is recommended only for light-duty carts under 500 lb total, short runs, or where omnidirectional maneuverability matters more than tracking 4 .

Above walking speed or under heavy load, four swivel is described as unstable 4 . Brake mode is a separate decision from swivel mix.

A wheel brake stops the wheel from rolling but does not control swivel position; a total-lock brake controls both rolling and swiveling and is recommended for heavy equipment, workbenches, server racks, machine bases and industrial carts 27 .

Where slopes, ramps or staff leaning on the cart are involved, total-lock on at least two casters is advised; for tow-line carts that are uncoupled and subject to bumping, four brakes are advised 4 . A total-lock caster provides mobility and parking control only.

It does not raise, lower or level equipment, so leveling or retractable casters are the correct choice where height adjustment or leveling is required 27 .

Normalize quotes before comparing price

Cost drivers include wheel size and load, tread and core materials, brake or lock system, mounting design, bearings and steering structure, OEM customization, and testing or compliance work 24 .

A quote that includes a central lock and one that includes a simple brake are not the same product, so the specifications have to be aligned before the prices mean anything 16 .

• ✓Quote every supplier against the same load, wheel diameter, brake mode, mounting dimensions, tread and quantity
• ✓Ask what the quoted unit price assumes: sample cost, tooling or customization charges, packaging, test reports and order quantity
• ✓Clarify lead time and total landed freight for bulk orders
• ✓Confirm the return policy: stock items are typically returnable, made-to-order items are not
• ✓Ask what warranty applies and what it covers

Decide what certification and test documentation to require

Several standards and test types are referenced in this market, but no source establishes a mandatory certification for 100–500 kg casters. ISO 22883 is referenced for industrial caster quality and safety, covering hand-pushed or power-dragged applications up to 1.1 m/s (4 km/h) and more than 50,000 fatigue cycles 17 .

One manufacturer describes a static test at 150% of rated load held for 24 hours and a dynamic test of more than 100,000 cycles at 5 km/h 15 . ICWM covers load and dynamic-rating methodology, while AGV-specific tolerances are typically written into the integrator's spec sheet rather than a caster standard 7 .

NSF certification involves regular on-site inspections and confirms public health and safety standards for materials and products 34 . Because no single source makes any of these mandatory for this class, the practical move is to decide what documentation your application actually needs and write it into the RFQ.

Ask whether the supplier can provide the test report or certificate for the specific product, not for the product family.

Where the sources disagree

Two disagreements matter enough to resolve before committing. The load-rating method changes the rating you write into the RFQ, and the four-swivel question changes the configuration.

Neither is settled by the sources, so both should be put to the supplier against your own duty cycle.

What the sources do not establish

• No source provides a complete dimensional standard or catalog of mounting configurations for 100–500 kg casters.
• No source gives actual unit prices at volume, MOQ figures, or lead times for 100–500 kg casters as a class.
• No source establishes a mandatory safety factor or load-rating basis from a governing standard for this caster class.
• No source provides test reports or certificates for specific 100–500 kg caster products.
• No source quantifies caster offset or swivel lead values, or their effect on maneuverability, for this class.
• No source gives a single washdown, steam or cleanroom class requirement applicable to 100–500 kg casters.
• No source provides RoHS or REACH compliance information for 100–500 kg casters.