When looking at various small fans (like those found in a computer or the bathroom) you often see in their specifications the type of bearings they use. And the typical values there are either "sleeve bearing", "1 ball bearing" and "2 ball bearing".
Now I can imagine what a "sleeve bearing" is - it just means that the axis of the fan is stuck in a hole, maybe with a bit of lubricant, and that's that. In essence, it means "no bearing". But what are "1 ball" and "2 ball" bearings? I know what a "ball bearing" is in general, but how do you make that with just 1 or 2 balls? I think that the very minimum theoretical amount would be 3 balls but in practice I don't think I've seen anything less than 6 or so.