This is a mount for bicycle saddle rails to a go pro or any other compatible items.
The main difference with all other commercial mounts is that this one is designed to mount on the end-area of the rails (the area that is usually angled around 45 degrees), which I needed because I didn't had enough saddle setback to mount it on the horizontal part of the rails as every other mount.
You will need a couple M5 Screws and Lock Nuts which you can get from home depot,
I have mine tightened at aroun 2nm. if you don't have a torque tool, just tighten it with your wrist do not use your arm as leverage. In my case this has been tight enough that the mount doesn't move even with large bumps, I have only used it on a road bike, is plastic so not sure how well it would hold on a mountain bike.