At first I didn't mean to do so many of them, but every time I told myself thats the end I've reminded some technique or tool, which I didn't tried before with gears.
After I finished over 100 of them I thought that it would be cool to be able combine inside and outside, so I cutted insides...
...and made few more outsides and corrected size here and there so they could all be replaceable with eachother.