Many surfboards now come with 5 fin boxes installed to allow the surfer to choose to ride the board as a thruster setup with 3 fins or a quad setup with 4 fins. This means that either 1 or 2 fin boxes will be left open while surfing. While this may seem inconsequential, it actually increases drag while also interrupting the flow off water as it passes over the concave(s) of the surfboard bottom and the fins.
These fin box fillers pop and screw in just like a regular futures fin. And they have a angled hole on top so you can pop them out easily using a fin key. I thought they would be hard to get out, but even on a brand new surfboard with tight fin boxes they went in and out easily.
10/10 would recommend.
