GoPro handle bar mount adapter
thingiverse
The perfect part for securing a handlebar mount on narrower poles is readily available! All it takes is a quick find, and you're good to go - just head over to the URL (http://www.thingiverse.com/thing:660751), click on the J-shaped link in grey, and voilà, your problem is solved.
Download Model from thingiverse
With this file you will be able to print GoPro handle bar mount adapter with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on GoPro handle bar mount adapter.