We are all part of a larger whole. The scope of the larger whole is sometimes difficult to fathom. In this case, these are pulleys, not cogs, and they have a bit of silicone or rubber to absorb shock and vibration. Smoothing out the bumps seems like a good idea in many contexts.
I like the way the translucent silicone looks. It’s always fascinating how industrial parts are beautiful objects with the right perspective and lighting.