magnetic building board-3D printed.

thingiverse

I probably would not bother too much with these, the dual pole hold downs are much more versatile and stronger and way faster to print. Added: I designed 3D printed version of the wooden hold downs, there is also a pad that fits on the bottom of the 3/16 screw and a convenient area for it to be store on the hold down. See Picture for examples. I used a 3/16 threaded rod for the screw downs, I brazed a flat washer on the bottom, but pack it up with a waste piece of balsa, so as not to damage the work piece being held down under pressure, One magnet per side gives 2.5kg of hold force, 2 per side was just over 6kg's. (I know each magnet has approx 6kg holding force, but that is force applied directly to the magnet to remove it from the board, taking into account the lever arm and mechanical advantage of the screw mechanism you get a reduced hold down, as indicated above)