This holder clips to an ikea KLUDD whiteboard and offers space for up to four ikea whiteboard markers although most other markers would probably fit as well. I used to put the markers on the shallow edge on top of the board but they keep falling off and there is room for only two of the four markers. Print it upside down for minimal overhang. 0.25 mm layer height worked fine for me but if you want something better-looking choose something smaller.