Well, to me, anyway.
You’ve all played pool on a coin-op table in a bar, obviously. Did you ever wonder how the table knows which ball is the cue ball? It has to be able to tell somehow, because after every scratch during play it returns the cue instead of trapping it with the object balls.
Turns out, there’s two ways.
One method involves a big-ass magnet and requires the cue contain enough iron for the magnet to pull it to one side and change its pathway inside the table. That’s pretty neat. (Click through; there’s video.)
The other method involves a cue ball that is fractionally bigger (2 and 3/8 inches vs the standard 2 and 1/4) than the object balls, and uses a slightly different mechanism to do the segregation that’s perhaps a bit easier to imagine since it’s size based.
This information has implications, though.
First, it means that home or premium table cue balls won’t work on coin-op tables, because in those sets (a) all the balls are the same size and (b) none of them contain iron.
Second, a bar owner who needs a new cue ball for his table will also need to know which kind of mechanism his table has, because there two types of cue balls and the iron one won’t work on a table that expects an off-size cue, and vice versa.
Interestingly, the first several billiard supply shops I found online didn’t even deal with coin-op cue balls; they were all about the home or premium market. I assume this is because a bar owner (or similar) is dealing with some local amusement vendor and not the Internet most of the time, whereas folks searching for “pool table supplies” online are looking to outfit their own billiard room.
No idea why this information charms me so much, but there it is. (Also: Magnets!)