10 speed smallest one on the back wheel.
Definitely not a drive cog from a bike wheel, the closest bike part would be a rear derailleur cog but I've never seen a metal one that I can think of. It does look like part of a chain drive system though, but it's too small for a bicycle chain. My first thought was a rowel from a spur, and it does look like one to me. I found a few similar on google images but the pics were really small and hard to make a match