Futures fin box to glass in to a foam or wood surfboard. Box is a little deep but the set screw should hold it in the right place.

The "thin wall" version I designed to cut down on plastic. It's plenty heavy duty enough and has the same size opening for a fin.

"Lowpro" is an attempt to make a box as short as possible, to fit in an extra thin board. I measured some 3d printed futures fins, but I can't guarantee that any given futures fin will fit this, it's well beyond the spec (at the very least, you may have to modify the slot in the rear so that the fin can enter at an angle).

I've printed lots of these. I've hit fins on rocks and shattered the fins, and these have held up. The one that I've broken comes from hitting a solid glass fin on a rock at full speed. Even then, they can be routered out and replaced.