Prices are for individual fillers.
Less drag! If you are riding a 5 fin setup and do not have these, get on it! They fill those empty holes.
Box Fillers are designed to be placed into empty fin boxes when not in use. This most commonly occurs when riding a 5-Fin setup as either a thruster or quad, since all 5 boxes are not utilized at the same time.
1/2" fillers fit in the back three boxes of a 5 fin setup.
3/4" fillers fit in the front two boxes of a 5 fin setup.