That's totally wrong. It produces a widget which can't be mounted.
The bug is, effectively, that the base wants to be on the other side.
That does involve sort of swapping the ends, but not like this.
This reverts commit
0fe8aba40e7d868e9d60a8af34933e392b8f108c.
end_thick = arch_thick;
-holes = [[[ 18.5, 4.5], [ 4.5, 21]], // left
- [[ 5 , 5 ], [16 , 21]]]; // right
+holes = [[[ 5 , 5 ], [16 , 21]], // left
+ [[ 18.5, 4.5], [ 4.5, 21]]]; // right
module ArchCircle(rad){
translate([0,-arch_to_chord])