I would recommend Quad Lock, their stuff is brilliant and top quality. It is expensive mind, but worth it! They do all sort of fixings, from handlebar (22mm) to mirror mounts (12mm like the handlebar cross brace), or adhesive mounts as I have used. I did put some self tapping screws in as well to be 100% secure, not everyones taste but it positions my phone in perfect view for Sat-Nav etc while riding.