Specifying Medium-Duty Casters: What Load Ratings, Wheel Sizes and Mounting Options the Evidence Defines

'Medium Duty' Names a Marketing Tier, Not a Load Range

Treat the duty-class label as marketing shorthand and decide the capacity figure yourself. One industry distributor classifies medium duty as roughly 500–1,500 lb per caster for industrial carts and racks, with light duty under 499 lb and heavy duty at 1,500+ lb¹⁴.

One manufacturer instead lists its medium-duty line at 100–190 kg and its heavy-duty line at 150–610 kg — the two bands overlap^1,19. No governing standard for the class label appears in these sources, so a spec written around 'medium duty' commits you to whatever each supplier's catalog means by it.

Write the required per-caster capacity in lb/kg into the RFQ and let the label play no role in qualification.

Make the Rating Comparable: Basis, Speed and Test Protocol

A capacity figure is only comparable across manufacturers when it names its load basis and test protocol. Dynamic and static ratings are distinct: one medical caster publishes 176 lb dynamic at 1.86 mph against 353 lb static — the same part with two numbers⁹.

Dynamic ratings run lower than static for the same caster and depend on the stated speed, so an unlabeled figure cannot be compared⁹. Protocol matters too: ICWM/ANSI-ICWM 2012 defines rated capacity as 3 mph continuous rolling over a minimum of 10 miles under rated load with defined failure criteria.

And two compliant 1,500 lb ratings should mean the same product¹⁹. A rating without protocol disclosure may use shorter distances or lower speeds.

So ask each supplier to state the load basis (dynamic or static), the test speed, and the protocol (ICWM or equivalent) before you compare quotes¹⁹.

Add Margin for Shock and Continuous Duty Before Fixing the Number

Steady-state cart weight alone under-specifies the caster. Shock spikes when a caster hits a threshold, dock plate or debris can reach 2–3x the static load for milliseconds — enough to dent bearing races, crack treads or shear kingpins²³.

In high-shock environments such as loading docks, outdoor yards and threshold crossings, one source recommends adding a 1.5x shock factor to the calculated load²³. For a 1,000 lb dynamic requirement that means specifying a 1,500 lb caster²³.

Duty cycle changes the picture as well: one source reports a 30–40% load de-rate for 24/7 operation versus 8-hour duty, pushing continuous-duty applications toward heavier construction^8,19.

Both figures are single-source screening values, not industry requirements — ask each vendor how they de-rate for your shock exposure and duty cycle rather than treating either as mandatory.

Wheel Diameter: What Medium-Duty Assortments Actually Offer

Published medium-duty assortments centre on 3"–8" wheel diameters, commonly with 2" tread widths — one distributor lists 3-1/4"x2", 4"x2", 5"x2", 6"x2" and 8"x2" options in its medium-duty line²⁹. Assortment scope varies by seller; another caster site filters collections at 3" to 5" diameters³.

Larger diameters carry more load and roll more easily over cracks, thresholds and uneven floors, though they need more space^3,10,21. No source in this set quantifies how load rating scales with wheel size within medium duty.

So choose the diameter for your floor conditions and clearance, then verify the rating that diameter delivers from the supplier's load tables^3,29.

Plate or Stem Mount — and Which Dimensions to Pin Down

Across independent sources, the standard mounting set for this class is top plate, threaded stem, grip-ring stem, expanding adapter and bolt-hole^3,11,21. Plate mounts bolt to a flat square bracket and give more stability for heavier loads; stems fit into a hole or socket, suit tubular frames, and install faster^3,21.

Decide the mount from your frame: bolted flat surfaces take plates, round tubing takes stems or expanding adapters^3,21. Only one distributor publishes standard medium-duty mounting dimensions — a 4"x4-1/2" top plate with a 3"x3" bolt pattern slotted to 2-5/8"x3-5/8", zinc plated²⁹.

No source establishes standardized plate or bolt-hole dimensions across manufacturers, so write your required plate size and bolt pattern into the RFQ and ask each supplier to match it²⁹.

Demand the Full Dimension Set Per Wheel and Mounting Combination

A caster is defined by interlocking dimensions, not wheel diameter alone — get one wrong and it will not bolt up, rides at the wrong height, or binds on floor obstacles²⁴. No source publishes a full medium-duty combination table, so require these dimensions per wheel and mounting combination before you order:

• ✓Wheel diameter and tread width
• ✓Overall height from floor to top of plate or stem shoulder — replacements must match, since even a small height mismatch across four casters causes rocking
• ✓Swivel radius, the clearance the caster needs to rotate 360°
• ✓Top plate length and width, or stem diameter and length for stem mounts
• ✓Bolt-hole spacing and mounting hole diameter

What to Verify at Quote: Lead Time, MOQ and Certification

Availability, volume pricing and certification are documented only as isolated supplier claims, so confirm each at quote. One caster retailer ships in-stock items the same business day, while brand-direct lines such as Hamilton, Colson and Albion follow manufacturer lead times confirmed on your quote¹⁵.

Volume breaks appear in this evidence only on one heavy-duty product — 5%/10%/15% at 50/100/200+ units — so ask whether similar breaks apply to medium-duty lines rather than assuming them⁶. One supplier states custom sizes carry mild MOQs with 7–10 working day lead times and factory load testing before shipment³⁴.

On certification, no medium-duty product in this set is confirmed NSF, ISO or ICWM compliant. One wheel line claims NSF approval and a 3-year warranty, but third-party versus self-declared status is a question for each supplier^2,19.

Where Published Medium-Duty Ranges Disagree

The published medium-duty bands do not even overlap, and one manufacturer's heavy band swallows its own medium band. That conflict is the strongest reason to quote capacity in lb/kg with a rating basis instead of the class name:

Before you request a quote

• Public sources do not settle this — put it to the supplier: no manufacturer in this evidence publishes a complete medium-duty line sheet combining load ratings, wheel sizes, mounting dimensions and heights in one place — request a full line sheet or per-combination spec sheet from each supplier.
• Public sources do not settle this — put it to the supplier: no source states whether medium-duty ratings are dynamic or static as a class; only individual products specify the basis, so ask per product.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.
• Public sources do not settle this — put it to the supplier: no source publishes standard grip-neck stem or expanding adapter dimensions — confirm against your tube ID with the supplier.
• If independent assurance matters, request current inspection reports and verifiable supplier credentials.
• Request the complete specification sheet with units, test conditions and configuration assumptions.