[Caio]

You were right. There are two types. But it's not double flanged or flanged. They make a square cut out in the chassis, and though the pieces are circular, they have a small square section just beyond the flange for the chassis. However, there are some that don't have it, which means they aren't being tensioned, and aren't being used for the drive. There are 76 with the square, so enough for 6 robot drives (lol) and the rest aren't.

Sooo, I'm assuming roller bearing blocks.