I have a classroom set of Micro:bits. To protect them and to make them easier to use in maker projects, I designed a case for them (https://www.thingiverse.com/thing:2098058), and this rack is meant for Micro:bits in those cases. I used one inch wide strips of magnetic tape to stick these racks on my classroom's magnetic whiteboard. (The magnetic tape I used came unstuck after a few days on one rack, so I attached the strips again with a quality super glue.) Double-sided foam tape or similar would let you mount it somewhere more permanently as well.