Cogs, wheels, cogwheels, cog wheels, sprockets, etc. ? Cogwheel is virtually identical to cog-wheel The OED uses the hyphen; Merriam-Webster omits it Finally, people mix these uses all the time I couldn't have told you the exact difference between a sprocket, a cog, and a cogwheel without looking it up Unless you're working in a highly technical context or enjoy linguistic trivia, I wouldn't worry