The Ortlieb Vario QL 2.1 bike bag includes a hook on a strap to be fastened on the bike's luggage rack somewhere near the wheel's hub.

However, many luggage racks don't have a bar or anything similar where the hook can be anchored. Leaving the hook unfixed is possible but causes the bag to shake heavily in curves and on loose terrain.

This fixture bar offers a solution for this problem. It is designed to be attached between the two tubes of a simple luggage rack (please make sure to read the specs below). As a side effect this part increases the stiffness of the luggage rack.

Specs:
The model is designed to be attached to a luggage rack with the two tubes having a diameter of ~10 mm and a ~40 ° angle.

To ensure a tight fit and also to protect a possible coating on the luggage rack tubes, the model allows a layer of ~1 mm between the tube and the printed part (in other words: instead of 10 mm a tube diameter of 12 mm was used). I used an old bicycle tube.

The screw holes have a diameter of 4.5 mm - I recommend to use flat head M4x20 screws and DIN 985 M4 lock nuts.

Customizability
For the (probable) event that your bike's luggage carrier is different to the specs above, I added a highly customizable FreeCAD file.

A lot of settings can be changed in the spreadsheet named v, most (if not all) other features are automatically changing if you edit the right sketches.

Feel free to leave me a comment in case you cannot figure it out yourself.