This mount allows you to connect basically anything to the top of the steerer tube of your bike. Use 3M double-sided tape, 3M 'Dual Lock' or rubber 0-rings to connect your phone, GPS or whatever else to the mount. The wear compensation screw allows you to adjust the tightness of the locking mechanism, as prototyped on my other mounts.
When you get this product, there will probably be some excess powder in the hinges and around the loose internal ring. You need to get this out either by washing the parts or working them free with your fingers. The hinge will be stiff at first, but once the powder comes out it should move very freely.
When installing the threaded lock ring for the first time, make sure you align the clips on the internal ring with the recesses on the lock ring. The internal ring should click on and stay there