This bracket allows for the attachment of a Garmin Varia rearview radar to the reflector/tail light mounting holes found on many Topeak luggage racks. It requires the K-edge "insert" peice to connect to the Garmin, 2 M3 nuts, 3 M5 nuts, and 3 angle-head M5 screws.
NOTE: a newer version of this is now available:
https://www.shapeways.com/product/YKGHCYR2E/garmin-varia-mount-for-topeak-racks-version-2. The new design is better suited to the updated Garmin Varia RTL 510 released in 2018 because it reduces the chance that the device will rub against the rear tire on some setups. This version is available in case it is still useful to anyone, but I will likely discontinue it at some point.