Both spellings are correct. "Caster" is the standard American English spelling for a wheeled industrial mounting assembly. "Castor" is the British and Australian English spelling for the same component. The two words refer to the identical product. American B2B and OEM specifications use "caster" almost exclusively.
- American English: caster (used in US industrial, MRO, and OEM specifications)
- British / Australian English: castor (used in UK, AU, and NZ standards)
- ANSI MH28.1 uses "caster"; ISO 22878 uses "castor"
- The "castor oil" confusion: both spellings predate the oil's name and are not related
- Search volume in the US is roughly 16x higher for "caster" than "castor"
- Both refer to the same wheel-and-mount assembly we sell at 844-439-4335
Caster and castor are two correct spellings of the same word for the wheel-and-mount assembly bolted to the bottom of carts, chairs, and equipment. American English uses caster. British and Australian English use castor. The product is identical. Spec sheets, OEM drawings, and ANSI standards in the US use caster. ISO and BS standards use castor. Pick by your audience, not your preference.
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Quick answer: which spelling is correct?
Both "caster" and "castor" are correct spellings for the same wheeled mounting assembly. They refer to the identical product. The two spellings split along regional English lines: American English uses "caster" almost exclusively in industrial, MRO, and OEM contexts; British, Australian, New Zealand, and South African English use "castor." Canadian English is mixed, with "caster" dominant in trade and "castor" appearing in older institutional writing.
- Caster (US): Standard in American industrial spec sheets, ANSI MH28.1, ICWM, RIA, and the Material Handling Institute style guides.
- Castor (UK / AU / NZ): Standard in British Standard BS EN 12530-12533, ISO 22878, and Australian / New Zealand AS/NZS heavy-duty references.
- Same product: A 4-inch swivel plate caster from a US catalog is the same item as a 100mm swivel plate castor from a UK catalog.
- No technical difference: The spelling does not change the load rating, materials, bolt pattern, or duty class of the part.
Engineer tip: If you are writing a spec sheet for North American buyers, use "caster" throughout. If you are writing for UK or Australian buyers, use "castor." Mixing the two inside one document is not technically wrong, but it reads as careless and can flag your RFQ as auto-translated. If you sell into both markets, build two versions of the cut sheet.
Where the words came from: 1748 caster vs 1789 castor
Both spellings trace to the English verb "to cast," meaning to throw, turn, or roll. The earliest dictionary citations of "caster" meaning a small swiveling wheel appear around 1748 in English furniture trade vocabulary, describing the small wheels under chairs and tables that let servants "cast" the furniture across a polished floor. "Castor" as the same furniture-wheel sense shows up in print around 1789, often as a stylistic spelling variant rather than a different word.
The split between the two spellings hardened during the 19th century as American and British English diverged on -er versus -or word endings (the same pattern that gave us "color" vs "colour" and "center" vs "centre"). Noah Webster's 1828 American Dictionary of the English Language standardized "caster" for the US market. British dictionaries kept "castor" as the primary headword, with "caster" listed as an American variant.
- Root verb: "To cast" — Old English / Old Norse origin meaning to throw, turn, or set in motion.
- 1748: First print citation of "caster" in the wheel-under-furniture sense.
- 1789: "Castor" appears in the same sense, both spellings competing for a century.
- 1828: Webster's American Dictionary locks "caster" as the standard US spelling.
- 1899: Oxford English Dictionary first edition keeps "castor" as the British headword.
- 2026: Both spellings remain correct; both appear in major dictionaries; regional preference is now the only deciding factor.
Same word, two coats: Caster and castor are not separate technical terms with different meanings. They are the same word with different orthographic conventions, the same way "tire" and "tyre" both mean the rubber ring on a wheel. A 1900 catalog from Sheffield reads "castor" on every page; a 1900 catalog from Cleveland reads "caster." The wheels look identical.
US "caster" vs UK "castor": regional usage today
In 2026, the regional split is essentially absolute in trade publications and OEM specs, and roughly 95/5 in consumer search. US industrial buyers, distributors, and OEMs use "caster." UK, Irish, Australian, New Zealand, and South African buyers use "castor." Canadian usage skews to "caster" (about 85/15 in trade) thanks to the cross-border industrial supply chain with US distributors. Indian English uses both, with "castor" slightly more common in older engineering documents and "caster" gaining ground in newer e-commerce.
| Country / Region | Standard Spelling | Trade Usage Notes |
|---|---|---|
| United States | caster | Used in ANSI MH28.1, ICWM, RIA, and all US OEM drawings. |
| Canada | caster (mostly) | Cross-border supply chain with US drives caster usage in trade. |
| United Kingdom | castor | Used in BS EN 12530, BS EN 12533, and UK furniture trade. |
| Ireland | castor | Follows UK convention in technical writing. |
| Australia / New Zealand | castor | Used in AS/NZS heavy-duty references and trade catalogs. |
| South Africa | castor | British convention dominant in industrial supply. |
| India | both | "Castor" in older engineering docs; "caster" in e-commerce. |
| Singapore / Hong Kong | castor (mixed) | British convention dominant; American spelling rising in B2B. |
Inside CasterHQ's daily order flow, we see roughly 1 in 50 RFQs use "castor" and the buyer is virtually always reaching us from a UK, Australian, or older Commonwealth-trained engineering background. We answer in their spelling. The order ships the same product either way. See the full anatomy and definition in our What Is a Caster? reference.
Which spelling industry standards use
The split between American and Commonwealth English carries cleanly into the international standards that govern caster manufacturing and testing. ANSI (American National Standards Institute) and ICWM (Institute of Caster and Wheel Manufacturers) write "caster" in every published standard. ISO (International Organization for Standardization) writes "castor" in its formal documents because ISO drafts originate in British English. The standards themselves describe identical products.
| Standard Body | Region | Spelling Used |
|---|---|---|
| ANSI MH28.1 | United States | caster |
| ICWM (Institute of Caster & Wheel Manufacturers) | United States | caster |
| MHI (Material Handling Institute) | United States | caster |
| RIA (Robotic Industries Association, AGV specs) | United States | caster |
| ISO 22878 | International (BS-rooted) | castor |
| BS EN 12530 / 12531 / 12532 / 12533 | United Kingdom / Europe | castor |
| AS/NZS heavy-duty references | Australia / New Zealand | castor |
If you are writing a spec for a US Department of Defense, FAA, or USDA application, write "caster." If you are writing for a UK MOD, CE-marked European, or Australian Defence application, write "castor." ISO and EN standards are the governing reference for cross-border equipment, and they use the British spelling. Our Industrial Casters Complete Guide walks through the duty classifications behind both spelling conventions.
Spec sheet hygiene: Mixing "caster" and "castor" inside a single document looks like a copy-paste error and can get an RFQ kicked back by procurement. If your buyer is American, use caster. If your buyer is British or Australian, use castor. If your buyer is global, pick one and stay consistent across the entire document.
Why "castor oil" isn't related to wheels
Castor oil and the castor (or caster) wheel share a spelling, but they have nothing to do with each other. Castor oil is pressed from the seeds of the Ricinus communis plant (the "castor bean"), and the name traces to a separate Latin root unrelated to the verb "to cast." The wheel sense of caster/castor predates the oil's English name in furniture trade vocabulary, and the two words ended up sharing letters by coincidence rather than common origin.
- Castor oil: From the castor bean plant; named in English in the 17th century via Latin and possibly through confusion with beaver glands ("castoreum").
- Castor / caster wheel: From the verb "to cast" (throw, turn, set in motion); named in English furniture trade around 1748.
- No shared root: The two words arrive at the same spelling from different etymological paths.
- No shared product: A castor wheel contains no castor oil. Castor oil is not used to lubricate caster bearings (lithium grease and synthetic NLGI 2 are standard).
- The confusion in catalogs: Older British furniture catalogs sometimes wrote "castor" for the wheel and "castor" for the oil on the same page, which fed the modern confusion.
If you came here looking for the oil: You probably want a different page. CasterHQ does not sell castor oil. We do sell wheels with sealed precision bearings that ship pre-greased with NLGI 2 lithium-complex grease. See the materials breakdown in our Caster Wheel Materials Guide.
Search volume + Google Trends data: which spelling people use
In US Google search, "caster" outpolls "castor" by roughly 16 to 1 for industrial wheel queries, and the gap is growing. Year over year US trend data shows "caster wheel" and "caster bolt pattern" gaining about 8% in monthly search volume since 2022, while "castor wheel" in the US is essentially flat. Globally the picture flips in the UK and Australia, where "castor wheel" outpolls "caster wheel" about 7 to 1 in Google UK and AU search.
| Query | US Monthly Volume (range) | UK Monthly Volume (range) |
|---|---|---|
| caster wheel | 33,000 to 49,000 | 1,800 to 2,400 |
| castor wheel | 2,200 to 3,400 | 14,000 to 22,000 |
| caster vs castor | 600 to 1,500 | 400 to 900 |
| how to spell caster | 200 to 600 | 100 to 300 |
For B2B distributors writing for North American buyers, "caster" is the keyword to use in product titles, H1s, meta descriptions, and product schema. Splitting traffic between "caster" and "castor" pages does not help in the US market because both Google and Bing already recognize the two as variants and serve the dominant regional spelling first. CasterHQ writes for the American market and uses "caster" throughout the site.
When to use caster vs castor in writing or specs
Pick the spelling that matches your audience, your spec authority, and your style guide. Stay consistent inside the document. The right spelling for an RFQ in Texas is "caster." The right spelling for an RFQ in Manchester is "castor." Inside a single document, never alternate. Inside a single brand voice, pick one and apply it across all pages, product titles, schema, and metadata.
| Use Case | Recommended Spelling | Why |
|---|---|---|
| US industrial RFQ or PO | caster | Matches ANSI, ICWM, and US OEM language. |
| US e-commerce product page | caster | Matches dominant US search volume by 16 to 1. |
| UK / EU industrial RFQ | castor | Matches BS, EN, and ISO standards. |
| Australian / NZ trade catalog | castor | Matches AS/NZS and Commonwealth convention. |
| Canadian trade document | caster | Cross-border industrial supply standard. |
| Global ISO-aligned spec | castor | ISO drafts originate in British English. |
| Academic furniture history paper | either (footnote both) | Both forms are historically attested. |
- Be consistent: Pick a spelling at the top of the document and never switch.
- Match the buyer: If your reader is American, use caster. If British or Australian, use castor.
- Match the standard you cite: If the document references ANSI, write caster. If it references ISO or BS, write castor.
- Match the brand: If your distributor uses caster across their site, use caster in your part of the supply chain.
- Do not mix: Mixing inside one document reads as careless and can flag procurement.
Sales tip: If a UK or Australian buyer emails an RFQ to our team using "castor," we reply using "castor" throughout. The product description, line items, and confirmation all match the buyer's spelling. It costs nothing and signals that we have read the request carefully. Try this on your own outbound and watch reply rates rise.
Related spelling confusions: caster wheel, castor cup, caster sugar
The caster / castor split shows up in compound terms too, and the regional convention carries through every compound. If you are writing for the US market, use "caster" in every compound: caster wheel, caster cup, caster bolt, caster brake, caster stem. If you are writing for the UK market, use "castor" in every compound. The exception is "castor sugar" (the British name for what Americans call superfine sugar), which is always spelled with the -or even in American writing because it is a proper culinary term borrowed from the UK.
| Term | US (American English) | UK (British English) |
|---|---|---|
| The wheel-and-mount assembly | caster | castor |
| The wheel only (sub-component) | caster wheel | castor wheel |
| Floor protector under furniture | caster cup | castor cup |
| The mounting bolt that holds it | caster bolt | castor bolt |
| Brake / lock mechanism | caster brake | castor brake |
| Threaded stem subtype | stem caster (see stem caster types) | stem castor |
| Superfine sugar (culinary) | castor sugar | castor sugar |
| Vegetable oil from Ricinus communis | castor oil | castor oil |
| The astronomical star (Gemini) | Castor | Castor |
Two compounds always keep the -or spelling regardless of region: "castor oil" (the vegetable oil) and "castor sugar" (the British culinary term, which Americans borrow as-is). The constellation star Castor in Gemini is also always spelled with the -or because it is a Latin proper noun. Every other compound related to the wheel follows the regional convention.
For specifying a swivel rig: If you write "swivel caster" in the US or "swivel castor" in the UK, both are correct. Compatibility, compatibility checks, and replacement logic are identical regardless of spelling. See Are Casters Universal? Compatibility & Replacement for the engineering side, and Industrial Casters Complete Guide for the duty classification reference.
Frequently asked questions
Is it caster or castor?
Both are correct. "Caster" is American English and is the standard spelling in US industrial, MRO, and OEM documents. "Castor" is British and Australian English and is the standard spelling in UK, EU, Australian, and ISO standards. Both spellings refer to the same wheel-and-mount assembly. Pick the spelling that matches your audience and stay consistent inside the document.
How do you spell caster?
In American English, spell it c-a-s-t-e-r. In British, Australian, New Zealand, or South African English, spell it c-a-s-t-o-r. Both spellings refer to the same product. Canadian English usually follows the American spelling because of the cross-border industrial supply chain. Indian English uses both, with castor more common in older engineering documents.
Are caster and castor the same thing?
Yes. When the word refers to a wheeled mounting assembly bolted under a cart, chair, or piece of equipment, "caster" (US) and "castor" (UK) refer to the identical product. The spelling does not change the load rating, materials, bolt pattern, or duty class. A 4-inch swivel plate caster from a US catalog is the same as a 100mm swivel plate castor from a UK catalog.
Why do British people spell it "castor"?
British English kept the older -or spelling for many words where American English shifted to -er during the 19th century, the same pattern that gave us colour vs color and centre vs center. Noah Webster's 1828 American Dictionary of the English Language standardized "caster" for the US market, and the British convention stayed with castor through the Oxford English Dictionary first edition in 1899 and into modern usage.
Is castor oil related to caster wheels?
No. Castor oil comes from the seeds of the Ricinus communis plant (the castor bean) and traces to a separate Latin root unrelated to the wheel meaning. The wheel sense of caster / castor comes from the English verb "to cast" (throw, turn, or set in motion). The two words ended up sharing letters by coincidence, not common origin. Castor oil is not used as a lubricant in caster bearings; sealed bearings ship pre-greased with NLGI 2 lithium-complex grease.
Which spelling do industry standards use?
ANSI MH28.1 (United States), ICWM (Institute of Caster and Wheel Manufacturers), MHI (Material Handling Institute), and RIA (Robotic Industries Association) all use "caster." ISO 22878 (international), BS EN 12530 through 12533 (United Kingdom and Europe), and AS/NZS heavy-duty references (Australia and New Zealand) all use "castor." Match the standard you are citing inside the document.
Should I use caster or castor in my product description?
Use caster if your buyers are in the United States or Canada. Use castor if your buyers are in the United Kingdom, Ireland, Australia, New Zealand, South Africa, or anywhere following Commonwealth English. Stay consistent across product titles, body copy, schema, and metadata. Do not split traffic by writing two pages targeting both spellings; Google and Bing already recognize them as variants and serve the dominant regional spelling first.
What is the plural of caster?
The plural is "casters" in American English and "castors" in British and Australian English. A four-wheel cart has four casters in the US or four castors in the UK. The pluralization rule follows the same regional convention as the singular form. There is no irregular plural; just add -s to whichever spelling you are using.
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Caster, castor — we ship the same part either way
Whether your spec sheet says caster or castor, we stock Albion, Hamilton, P&H, Colson, Faultless, and Durastar. Same-day RFQ response from our Mansfield, Texas warehouse. Talk to a real engineer.
Shop All Casters Call 844-439-4335Jordan Wilson
Jordan runs CasterHQ from a Mansfield, Texas warehouse stocking Albion, Hamilton, P&H, Colson, Faultless, and the in-house Durastar series. He has spent 15+ years specifying replacement and OEM caster systems for material handling, medical, food service, defense, and aerospace customers across North America, including ICWM-rated retrofits when brands discontinue parts.