A flat base, 40mm in diameter.
I've added cross-beams beneath the base because, in my experience, the main problem when printing bases is they are prone to warping because of the relatively large thin flat surface, specially when using ABS-like or water washable resins, and beams prevent this issue at the cost of very little extra material. This also made it easier to add a slot for a 3x2mm magnet to use alongside magnetic trays, as well as providing a better surface to glue larger magnets if desired thanks to the curvature of the cross.
