Printed several of these this solid, long face down, with white Hatchbox PETG and they work great.
The interior gap measures 9.5mm and has a slight chamfer at the top. Went through a few iterations and this fits our shower glass perfectly: snug enough to avoid any front-to-back wobble/clank but just loose enough to slide horizontally for easy repositioning.
The author hasn't provided the model origin yet.