Modification of the Nut_Ring

We live in a big world - I live in Germany and bought the coupling nut at a hardware store nearby. Unfortunately, the outer diameter of the  nuts (flat to flat sides) is not 13 mm , but 11 mm. Therefore, I made adjustments to the recesses in the component. 
I found the list of different coupling nut sizes for reference. I don’t know why the outer diameter of the M8 coupling nuts is smaller than that of the corresponding bolts, as it is actually 13 millimeters here.

Maybe this is useful.
Happy printing

Modified for a smaller face to face diameter of the Couling nuts. (11 mm instead of 13 mm)