Originally Posted by SlickGT1

The running board, OE ones come with their own wheel well plastic. If you look at the running boards, they transition into the fender wheel arches. These are unique to the running boards. The IS flares can be moved over from your non RB wheel arches, to the RB arches.

As a matter of fact, you cannot buy RB with the IS flares. Those are separate part number, and usually people just swap over the flares from their setup.