Base 3x3 for dungeon blocks system with magnet slots for 5x2 magnets added to magnetize the grid for easy snapping. There are two slots each side one for N and one for S polarity, doesn't matter which one is which as long as you stick to it for all grids.
The grid is also slightly bigger than original one - about 1.5mm bigger overall than original to account for any size imperfections of blocks that make them stick out when all in the grid.
The author marked this model as their own original creation.