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What's the name for a kind of gear that slips over the top of another gear and can drive/turn the gear it's surrounding?

I'm making a handcranked flashlight with my 7 year old. We're thinking of using a stepper motor with a gear on the end from an old printer, something like the one pictured. I've seen this kind of crank flashlight made with just a 'female' gear embedded in the crank handle, that slots right over the 'male' gear (as pictured here). That's the best way I can describe it. What's the name of this kind of gear? One that would slot right over the top of the gear in the picture below and be able to drive it? I can't seem to find what I am looking for anywhere, any ideas? If I knew it's name then I could search for it. Thank you!

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Edit** What I looking for is kind of like this internal spur gear (the image below), but with that outer ring FITTING REALLY TIGHT around the inner spur gear, with the number of cogs matching exactly (not like this picture, where the outer ring is really big compared to the inner gear).

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    $\begingroup$ If the outer ring exactly fits the inner gear, it's not a gear but simply a mating part. The inner gear no longer acts as a gear either but just as a toothed bushing to mate to the "axle" it's attached to. $\endgroup$ – Carl Witthoft Mar 27 '17 at 15:16
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    $\begingroup$ The word you might be looking for is "splines" which refers both to "teeth" cut in a shaft (a splined shaft) and the internally toothed bore (usually a push fit) that slips over it. $\endgroup$ – Brian Drummond Mar 27 '17 at 20:13
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I would call it a splined crank (i.e. a crank/handle that has a splined socket on one end -- like on some higher-end bicycle cranks).
In your case, it seems that you want to place the splined end of your crank/handle onto the spur gear that is mounted on the stepper motor shaft.

Another application of such a lever is a handle that is used on a water valve (e.g. an outside water spigot handle or some shut-off valve handles that are used under sinks for supply lines or for water heater supply lines). Of course, those handles are round & not in a crank shape like your application seems to require.

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Internal spur gear is a pretty good name for it, actually. In the context of a planetary gear, this would be called the ring gear. But since this is not a planetary, I would just call it an internal spur gear. Boston gear sells them http://www.bostongear.com/products/open-gearing/stock-gears/spur-gears/internal-gears and I'm sure a number of other places do too.

Since this sounds like a take-stuff-apart and re-use it kind of project, you might consider using an old cordless drill. Those almost always have a small planetary gear transmission in them. You can reuse the motor and transmission as-is to make a small generator out of it.

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    $\begingroup$ I think you misread the question (or he edited it since you answered :-( ). $\endgroup$ – Carl Witthoft Mar 27 '17 at 15:17

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