Thinvik Aluminum Alloy Bike Computer Stem Mount for Garmin Edge 820 810 800 520 510 500 25 - Angle Adjustable,Hinge Feature

The Stem Mount simply replaces the standard 5mm spacer on your steerer tube for a clean and very tough mount. The stem mount is made from CNC-machined aluminum, so it can take a beating and it won't flop around like a plastic mount. It works best with 0- or negative-degree stems, but can be used with riser stems if you have room for additional spacers. The Stem Mount was originally designed for mountain bikes but can be used for road bikes, as well.

from Consumer Electronics Store http://cestore.net/gps-navigation/gps-system-accessories/vehicle-mounts/Thinvik-Aluminum-Computer-Stem-Mount.html?pid=B07C8GTKCD