The metal version works with precise 16 mm ball bearings. The glass version was made to work with slightly bigger glass marbles (d = 16.5-17 mm)
The best stiffness of P1 is achieved with aligned rectilinear infill along the long axis.
Category: Household
The author remixed this model. Imported from Thingiverse.
I added two railings to keep the balls from falling out.