3/8'x3/8" magnets are used to hold a mount onto the backside of the Centauri Carbon that accepts SC5700/5800 model vacuum cleaner HEPA filters.  I use an M3 plastic screw to hold it down.  STEP file provided so you can easily change sizes.  It's the cheapest HEPA filter I could find domestically in USA (~$5 Home Depot).  It's a washable filter, which is a plus.