The two main sizes of blue wheels used are 75mm and 100mm. They are also available in 63mm and 120mm and sizes upwards of that I believe. When it comes to attaching them, if they've got a nut fitted into the centre of the wheel it is simply a case of screwing the wheel directly on to the output shaft of the drill motor. As a securing method, the reverse-threaded screw that comes with the drill that holds the chuck on can be screwed back in with a washer on it to stop the wheel unscrewing.

Quite simple and allows for relatively straight-forward maintenance.