This mount allows you to mount your GoPro to the top of your DSLR using the hotshoe mount. It's helpful if you want to use your GoPro for POV video footage while you're shooting, etc. It's also really useful for traveling, keeping your GoPro firmly attached to your camera and making it harder to lose/steal. When not it use, the camera folds down nicely against the top of the camera.
You'll need to print one of each of the hotshoe, knob, and nut holder. You'll also need 1 M4x25 hex head bolt and 1 M4 nut for the knob and screw. I prefer to use the printed knob and screw as opposed to the stock GoPro one because it's smaller and I don't need to take my other GoPro mounts apart.