Phone holder with rubber band

This is a phone gripper for a 1/4-20 mount screw.
Instead of using an additional screw-and-nut I used a rubber band. There's a groove for the rubber band to go on the top and bottom parts.

The top part has a mechanical constraint to keep it straight w.r.t the bottom, as well as a constraint to keep it from closing all the way down, this way the rubber band keeps its tension.

Sorry that I can't grab a pic with the phone in it, that's because I use the photo to take the picture. But you get