What would you consider a.......

Medium size throw? Undersize? Full size? I’m thinking 50 and up diameter is under, 50-52 is medium, and 53+ is full size. What do you think though?

51 and under is Undersized

51.1 to 53 is medium

and 53.1 and up is full size

But that is just me.

What about width and weight? It looks to me like 40mm is about mid-range width and 65gms is the average weight. Both of those seem to make as much difference as diameter as to how a yoyo throws and plays IMHO.

Yes, I would say 65 is the average weight. However, weight is a little more arbitrary. Yoyos can also play floaty or heavy, so weight is really hard to represent in a number or an average.

A yoyo is categorized as either undersized, medium, or full size by it’s diameter. I would say that what DYonch said is right. If it’s 49mm and 69 g, it’s still considered undersized. Same if it has a big width.