This kit requires a compatible BUP mount base.The BUP RTL510-515 SL mount arm positions the radar horizontally for clearance below the mount point.
Tether for Varia RTL 510 - Varia Series - Cycling - Garmin Forums
Horizontal Mount Arm Kit (SL) for Garmin Varia RTL510 and RTL515 (Includes Tether)
Direct Mount Base for Syncros Saddles
Shimano Bike Seat Saddle Mount for Garmin Varia & GoPro
Horizontal Mount Arm Kit (SL) for Garmin Varia RTL510 and RTL515 (Includes Tether)
Review: Garmin Varia RTL515 – 8/10 – Reliable alert system for being overtaken, with a very good rear light
Cestbon Radar Bike Mount for Garmin Varia Rtl510 515 TL300 and Garmin Varia Rearview Radar Tail Light. Saddle Bicycle Mount : Electronics
Direct Mount Base for Trek Bontrager Blendr Equipped Saddles
Varia Seat-post Quarter Turn Mount
Specialized Bike Seat Saddle Mount for Garmin Varia & GoPro