Total-Lock Casters in a Medical Equipment RFQ: What to Specify, What to Demand as Evidence

First decide whether the RFQ must demand total-lock at all

Four lock mechanisms are sold under overlapping names, and they are not interchangeable 10 . Total-lock stops wheel rotation and swivel together from one foot pedal; brake-only stops wheel rotation only; swivel-lock holds direction but lets the wheel roll; directional lock indexes the swivel at fixed positions 10 , 21 .

A wheel-only lock also has lower holding force than a total-lock mechanism and wears the wheel surface at the brake contact point. It is a different duty, not a cheaper version of the same one 20 .

You should write the lock mode into the RFQ as a definition, not a product name: "locks both wheel rotation and swivel, engaged by a single foot pedal". State explicitly that wheel-brake-only and swivel-lock mechanisms are not acceptable substitutes 10 , 21 .

Where the equipment must be completely immobile when locked, total-lock or a central lock is the indicated choice. If only rolling must stop, a side or cam brake suffices, and if only direction must be fixed, a directional lock suffices 9 .

If every caster must lock instantly rather than one at a time, the answer is a central locking system rather than individual total-lock casters 9 . For patient-contact mobile equipment, the industry-standard interpretation is total-lock on all four corners; for non-contact equipment, at minimum total-lock on two diagonal corners 7 .

That is an interpretation rather than a quoted clause. Treat it as the default you write in and confirm against your own regulatory pathway.

Write the load clause so quotes are sized on the same basis

A rolling application is governed by the dynamic rating, not the static rating. The dynamic figure is typically 60-75% of static and is the number that tracks service life 3 .

The ICWM dynamic rating at 3 mph is described as the industry-standard procurement reference. Naming a reference speed in the RFQ is what makes two suppliers' ratings comparable 3 .

Sizing on total load divided by four is optimistic. On uneven or worn floors one of four casters is routinely off the ground through frame racking or floor slope, and the remaining three absorb the full load.

The procurement-safe assumption is total load divided by three 3 . The same caution applies when a caster is retrofitted onto an existing platform: recalculate per-wheel load on the three-wheel dynamic method rather than reusing the rating of the caster being replaced 13 .

A worked instance shows how a margin is applied. A 900 lb loaded container on four casters gives 225 lb per caster, and a 30% safety factor points to casters rated at least 290-300 lb each 11 .

Note that this is one source's illustration, not a governing figure: another source questions whether a 2x safety factor is enough and recommends the divide-by-3 basis instead 3 . The sources do not agree on a single mandatory safety factor.

The RFQ should require the supplier to state the per-caster dynamic rating and the calculation basis behind it, and you should declare your own margin rather than assume the supplier applied one.

Fix the mounting interface and dimensions before anything is quoted

A caster is not described by its nominal wheel diameter. The assembly is defined by wheel diameter, wheel width, overall height, swivel radius, top plate size, bolt-hole spacing and mounting hole diameter, and every one of them has to fit the equipment 24 .

Get one wrong and the caster will not bolt up, will ride too high or too low, or will bind on floor obstacles 24 . For a replacement, measure wheel diameter, wheel width, overall mounting height and mounting type, and confirm the bore diameter if the wheel runs on an axle 25 .

Mounting type is a fork in the specification: plate mount suits equipment with existing mounting holes, threaded stem suits equipment with an existing threaded hole, and overall installation height must be re-checked either way 13 .

Retrofitting total-lock casters onto a cart that currently has brake-only casters is usually a one-for-one replacement if the mounting plate size matches one of the common patterns. 4" x 4-1/2", 3-1/8" x 4-1/8" or 4" x 4-1/4" — with plate size, bolt pattern, mount height and load rating confirmed before ordering 7 .

Put the dimension set in the RFQ as a required drawing or table. Ask the supplier to confirm each value against your frame rather than quoting a catalogue size.

Specify the wheel compound by name and its floor behaviour

Wheel compound drives load range and floor behaviour, and the two common medical choices sit in different bands. Polyurethane is listed at roughly 50-2,000 kg with low rolling resistance and good floor protection; nylon at roughly 100-3,000 kg with high rigidity, chemical resistance and high-temperature stability on flat ground 4 .

Across a wider catalogue the compounds offered run from PU and TPR through nylon, phenolic, rubber, cast iron, polyolefin and 304/316 stainless steel, with wheel diameters from 1" (25 mm) to 12"+ (300 mm+) and loads from 25 kg to 2,000+ kg per caster 12 .

Where ESD control is part of the requirement, conductive compounds exist: conductive TPR and nylon medical casters are offered, for example a 3-inch, 80 kg threaded-stem swivel caster with a 75 mm wheel and 95 mm installation height in M10/M12 stem sizes 22 .

That listing establishes availability, not a resistance limit — the sources give no ESD resistance band for medical use. The RFQ should require the supplier to state the compound and the measured resistance rather than you writing a threshold you cannot support.

Write the clause as compound name plus the behaviours you need stated: load range, floor protection and marking behaviour, and, where ESD applies, the conductive compound and its measured resistance 4 , 12 , 22 . The sources give no quantified rolling-resistance values, marking test results or cleanroom classifications, so those cannot be written as numeric acceptance criteria.

Name the test reports you will accept as a condition of award

The sources describe test methods rather than a single pass/fail table, so the RFQ has to select the parameters and require the supplier to report against them 6 , 14 . Require these reports with the quotation, not after the PO:

• ✓Dynamic cycle test over tens of thousands of rolling cycles at target capacity
• ✓Impact test at 2x target capacity, dropped vertically onto the mounted caster
• ✓Static load test at target capacity
• ✓Drop test from 30 cm onto a steel plate, repeated 10 times
• ✓Obstacle impact against a 5 cm step at 8 km/h
• ✓Salt spray per ASTM B117 for 72 hours on metal parts
• ✓Chemical exposure across pH 2-12

Fix the commercial terms and documentation package before you ask for prices

A central-lock quotation and a simple full-brake quotation are not comparable, so the specification has to be normalized before prices mean anything 15 . Ask every supplier to quote against the same load, wheel diameter, brake mode, mounting dimensions, tread requirement, quantity and documentation request 15 .

The cost drivers that move a quote are wheel size and load, tread and core materials, brake and lock system, mounting design, bearings and steering structure, OEM customization, and testing and compliance. You can pin each of these down in the RFQ rather than leaving it to the supplier's assumption 17 .

Customization is where the commercial terms shift.

One manufacturer states custom caster MOQ at 2,000-3,000 pieces depending on tooling complexity, falling to as low as 500 pieces for simple changes such as colour or logo, with sample lead times of 7-10 business days for standard modifications and 15-25 business days for fully custom designs requiring new tooling 29 .

Those are that manufacturer's own programme terms, not an industry schedule. Ask each supplier to state its own MOQ, tooling and sample charges, lead time, and the order quantity behind the quoted unit price 15 , 29 .

For OEM projects, sample testing and drawing confirmation are often worth more than a small unit-price difference. Make sample approval and drawing sign-off a gate before production rather than a post-award formality 15 .

Vendor qualification evidence to require as a condition of award

A supplier who cannot produce documentation cannot be compared on anything except price. Require these with the quotation:

• ✓Third-party test reports from a recognised laboratory such as SGS or TÜV
• ✓Material certification such as FDA or REACH
• ✓Actual application case data from comparable medical equipment
• ✓Traceability documentation covering the supplied lot
• ✓Receiving, in-process and finished-device acceptance records
• ✓Process validation records for any special process
• ✓Sample and drawing approval confirmed before production

Where the sources disagree, and what you must verify yourself

What the sources do not establish

• No source quotes the operative clause text of IEC 60601-1, IEC 60601-1-2, ISO 13485, FDA guidance, ANSI/BIFMA, EN 12527/12528/12529/12530 or ISO 22882/22883/22884/22885/22886 for caster locking, so the RFQ cannot cite a specific clause as the mandate.
• No locking force, torque or release force values for total-lock mechanisms are published in this evidence, so no numeric lock-force acceptance criterion can be written.
• No source states how the locked condition changes a caster's load rating, so the RFQ cannot specify a separate locked-condition rating.
• No harmonized acceptance-criteria table or ISO 22882 dynamic-test pass/fail limits are available, so the buyer must select parameters from the reported test methods.
• No quantified rolling-resistance, floor-marking or cleanroom-classification data for wheel materials is given, so those cannot be written as numeric criteria.
• No unit prices, tooling costs or volume price-break tables for medical total-lock casters are provided, so no target price or price-break structure can be pre-set.
• No source establishes that any caster supplier holds ISO 13485 certification or FDA registration, so certification must be requested as evidence rather than assumed.
• No ESD resistance limits for conductive or antistatic casters in medical environments are given beyond product availability.
• No source addresses the effect of total-lock casters on equipment stability during patient transfer, or ADA/ICC A117.1 repositioning requirements beyond a general statement that equipment in accessible routes must be repositionable by one person.