* So you can use 1/2\" base fins in 3/4\" boxes * Do your fins sit too low in the boxes? * Bring Fin to correct height * Durable Plastic * White Colour * 1x shim included The Futures 1/4\" Fin Box Shim is used for when you have a fin you want to use that has a 1/2\" base but you want to use it in a 3/4\" box. You will know if you need these shims when you put your fins in your board, do they sit too low? If yes then you definitely need a 1/4\" shim to bring them up to the correct level so that they can perform. Essentially you should only have this problem with your quad rear fins as all futures quad rear fin bases are made to be 1/2\" deep but if you should have 3/4\" deep boxes then this is where you will have a problem, this is when you need the 1/4\" shim filler.