We have two tags: cog and sprocket

neither are described. As far as I know, cog and sprocket are the same thing, but there may be a technical distinction that I'm not aware of.

Should I make this a question: What is the difference between a sprocket and cog?

If none, should we make the two synonyms?

  • AFAIK one's American word, the other is a European/English word for the same thing. But everyone uses Cassette for multiple of them, and Block is only used in the UK amongst older riders.
    – Criggie Mod
    Jan 12, 2017 at 22:25
  • Ok, merged them.
    – freiheit
    Jan 15, 2017 at 5:43

3 Answers 3


Technically... cogs are the teeth on a sprocket or gear. But the word also means "cogwheel".

A cogwheel is... basically any wheel with teeth (cogs).

A gear is a wheel with cogs that mesh with the gears of another wheel.

A sprocket is a wheel with cogs that mesh with a chain (or belt or tape or film or whatever). Just like a pulley, but with teeth that mesh somehow.

A typical bicycle doesn't have any gears on it, just cogwheels that are sprockets.

On the site: I think "sprocket", "cog" and "gear" are all used to mean the same thing and merging those tags would make sense.

UPDATE: is now merged into (with synonym).

  • Q: "what gear were you in at the time of the accident?" A: "black Raphla compression top, Castalri bib tights, and white Zoom shoes" based on this old chestnut lawvibe.com/… about the 6th one down.
    – Criggie Mod
    Jan 12, 2017 at 23:17
  • @Criggie I thought all that was "kit"? Are you telling me people use "gear" to describe that, too?
    – freiheit
    Jan 12, 2017 at 23:18
  • Are the toothed wheels in a freewheel cogwheels, or do they have yet another name :)
    – Móż
    Jan 12, 2017 at 23:22
  • People are using "gears" to talk about gearing in general, so I wouldn't make it a synonym of the cog-sprocket cluster. :-)
    – RoboKaren
    Jan 12, 2017 at 23:25
  • 1
    We might want to rename "gears" to "gearing" and add a redirect synonym.
    – RoboKaren
    Jan 12, 2017 at 23:26
  • @Móż The toothed wheels in a freewheel are cogwheels, and are also sprockets (sprocket being the specific type of cogwheel which applies to them). Jul 5, 2022 at 15:09

In wikipedia, Cog is defined as

A cog is a tooth of a gear or cogwheel or the gear itself.

Emphasis added.

Sprocket is defined as

A sprocket or sprocket-wheel is a profiled wheel with teeth [...] that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are smooth.

Sprockets are used in bicycles ...

Emphasis added.

A cog is not a sprocket. If we are to retain the Cog tag then it should be made a synonym of Sprocket. While that is technically inaccurate, it would support how non-technical people use the terms.

  • OK, so sprocket should be the main entry and cog a synonym. Sounds good to me! Someone with mod-authority, please make it so!
    – RoboKaren
    Jan 13, 2017 at 3:46
  • 1
    If I understand the definitions, all sprockets are cogs, and some cogs are sprockets. I agree that "sprocket" is probably the better tag to stick around, with "cog" merged in as a synonym. But I think it's a good idea to give people another day or two to notice this post and comment before we make it so.
    – freiheit
    Jan 13, 2017 at 4:29
  • @freiheit - no I think that's incorrect according to the definition. "Cogs" only interact with other "cogs" (or gears); while "sprockets" only interact with chains. Since our sprockets only touch chain, they are sprockets and not cogs. But this is prescriptive use and bicyclists have their own lingo.
    – RoboKaren
    Jan 29, 2017 at 2:59
  • 1
    @RoboKaren Yeah, but the purpose isn't defining these things just right; the purpose is getting things that are about the same topic tagged the same way. And cyclists definitely use both "sprocket" and "cog" to refer to the same thing.
    – freiheit
    Jan 31, 2017 at 3:21

Within BMX, "sprocket" always means a front gear ring with either a single hole (bolt drive) or spline drive, the kind that one-piece and freestyle three-piece cranks use.

I think it counts for something that this usage is ubiquitous and well-understood in BMX while cog versus sprocket is ambiguous elsewhere. Personally I never use "sprocket" to mean anything other than the BMX usage for this reason, although I wouldn't go so far as to say other usage is wrong. It's all arbitrary, but I feel disregarding the BMX terminology outright shows limited perspective.

  • From what you say, I'm getting that a BMXer would understand sprocket to mean the front ring. What do they call the rear sprocket / cog / thingy?
    – andy256
    Jan 20, 2017 at 2:31
  • A front ring that's bolt drive or spline drive. If it's got chainring bolts then more erudite BMXers call it a chainring. BMX-oriented wholesalers and retailers follow those usages too. Rear gears are freewheel if it's a freewheel, cog if it's a cassette cog, or driver if it's a one piece driver, as in most real street/park/dirt bikes. Jan 20, 2017 at 6:10

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