I think I understand what you're asking - more to do with the mounting holes.
The rad mounting is based on fan size and the fan mounting "screw/bolt" holes, not the width of the rad.
So for a 240 rad you would need the 240 flex-bay rad mount,.
Likewise for a 280 rad you would need the 280 flex-bay rad mount
Is that what you're asking about ?
and don't forget the the extra bay needed "Note: When installing a radiator it will stick past the mount in one or both directions. Please plan accordingly."
Edited by fast_fate - 3/5/15 at 6:41am