3rd Generation Freewheel

Sorry - How does one tell what generation / version of their “free wheel”?

I purchased a spare Aluminum Freewheel when I was in the USA - from my travels. So I assume that’s 2nd Generation. The plastic is 1st Generation? So what is 3rd Generation - how does one tell?

This is what I am referring to (pic from amazon.com)

Top is aluminum
Bottom is the plastic one.