COMPATIBLE with Garmin Varia Light/Radar RTL510, RTL515, and RVR315. The Varia adapter can be removed and the seatpost mount can be used as a rear GoPro or Action Camera mount (GoPro adapter not included). The mount fits seatposts with diameters of 27.2mm, 30.9mm and 31.6mm. Plastic spacers are included to fit seatposts smaller than 30.9mm. WIDE RANGE OF ADJUSTABILITY. Our seatpost mount can be adjusted left and right as well as up and down to get the best possible rear visibility to oncoming vehicles. Since our Varia mount is seatpost mounted, you can free-up your bike's saddle for a saddle bag or other accessories. MACHINED ALUMINUM for increased durability and high quality build. Our mount has only one screw connector and a hinge for better stability and ease-of-use. This design ensures that the mount stays on securely on any terrain at any speed. LOW PROFILE DESIGN and LIGHTWEIGHT. Weighs only 33 grams! The low profile design also reduces the chance of contact with your legs while cycling. PLEASE NOTE that some Action Camera GoPro adapters have varying thickness. If your adapter is loose when used with our seatpost mount, simply use a screw washer (not included). SATISFACTION GUARANTEED. If for any reason you are not happy with your purchase, please let us know and we will do what we can to make it right. Fully Adjustable Quarter-Turn Seatpost Bicycle Mount for Garmin Varia Radar RTL510 RTL515 RVR315 and GoPro Action Cameras