It's a pity that they got the orientation of the rollers wrong.

The wheels should have been oriented either like this:

      ___
  [\]|   |[/]
     |   |
  [/]|___|[\]

or like this:

      ___
  [/]|   |[\]
     |   |
  [\]|___|[/]

instead, they managed to mount them like this:

      ___
  [/]|   |[/]
     |   |
  [\]|___|[\]