I got a Thule cargo box for free, but it came with the narrow spacing for round bars. I made this part to have it fit aero bars. Print with many walls (I used 15), and many top and bottom layers. Use PA-CF, PETG, ABS, or ABS. PLA will melt in the sun.
This needs eight 7/16 washers to put under the Thule 6mm carriage bolt to distribute the load.
PA-CF might shrink and make the bolt not fit. If so, try the enclosed model for PA-CF as it has 0.75mm larger holes.
The author marked this model as their own original creation.