Allows you to cut ND Filters such as this one: https://www.amazon.com/Rangers-Graduated-Adaptors-Carrying-Cleaning/dp/B019RT2GRY and insert it to the slot provided. I've always had a problem with other GoPro mounts available such as when using SuperView, corners of the mount are seen, especially when I put ND filter in-between. The filter also scratches the lens cover when sliding it or when my quad crashes. And that is why I made this mount to solve those two major issues that I was having before. I made it ultra wide so that sides are not visible. The slot itself protects the lens cover from scratches. Please let me know if you have any questions or reviews. Thank you!