The hole in the base of the MPMD allows air from the fan to blow onto the heated bed and cool it down. I had originally covered it with a piece of card but wanted something a little better. So keeping with my magnet theme, I designed a magnetic cover. It uses 3 10mm neodymium magnets to hold the cover against the base.
Added a 12mm magnet version if you prefer to use them. These are actually 12.25 but if your printer is not calibrated your magnets may not fit depending on the actual magnet size and how far off you printer is.
Added a 13mm magnet version if your 12mm magnets are larger than 12mm
You may need to glue the magnets in. The actual design is 13.25mm
EconoFil (filaments.ca) PLA