I wear glasses. Specifically, titanium rimless glasses. The kind with the thin flexible arms. When I go to see a 3D movie, keeping the plastic 3D specs given to me by the theater on my face becomes a hassle. They always fall off, and I have to reposition them several times during the movie. This is a design for the common realD 3D glasses used by most theaters. The clip slides onto the arms of the 3D specs, and the arm of my glasses fit into the notch on the bottom, keeping them nice and stable. Printed in PLA with 20% infill. The infill percentage likely doesn't matter all that much on a part so small.