Holds three (3) Sakura Koi Coloring Brush Pens. This is enough to completely fill a Gridfinity bin but still allows modularity. Also contains a small flat section in the excess space for labels if needed. Pens fit with a snug but easy to remove fit. No magnet holes, but F3d file is included. I am not a professional CAD user, so it may not be perfect. I have printed 17 of these bins to fit 50 pens (set of 48 plus 2 blenders) and all the bins work well. Printed with 10% gyroid infill on a bambu X1C and otherwise default settings.