Some bikes don't have round bars, and Rocky Creek's Phone Mount with USB Charging Port needs to mount to a round bar. Here is a solution. This extension mounts under the mirror stem on "most" bikes using handlebar-mounted mirrors. The diameter of the hole in the mount is 10mm. Unscrew your mirror, position the mount at the base of the mirror mount then screw your mirror back onto the mount.
Note: Before ordering, please check that the diameter of your thread at the end of your mirror is 10mm.