The rollers go directly onto the base block (either on the bath base or on the rods if you have a Lift) for 2500 series tanks. The 1500 series tanks need the rollers on offset arms that point inwards towards the tank. This puts the rollers higher and closer to the rotating axis. So no arms for the 2500; 1500 need arms.
If you try running the tank without support I would expect it to fall off the magnet or the Lift at some point.