The purpose was to make a slotted bowling ball ring that could be easily put onto the straps of a bowling bag.
I printed with cheap PETG 240C, 50 speed and .2 or .3 resolution at 60% infill. The slot introduces some natural spring effect. Mine have 3-4 outside/top walls and a triangle infill pattern.
PLA and ABS should be fine. I think I will try one in TPU with low infill ~15-20%.
I hope this helps someone!