To be precise, that’s a cogwheel. There are six cogs around the cogwheel in your image. The word “cog” refers specifically to the teeth around the wheel, not the wheel itself. The cogwheel may be colloquially called a cog, but it’s technically inaccurate; If you told a watchmaker that their watch was missing a single cog, it would have a very different meaning than if you told them it was missing a single cogwheel.