I designed this to hold 2.25in x 3.5in (57mm x 89mm) cards that I had laying around.  It could be scaled up to fit full-sized index cards. The pencil tray prints separately and will need to be glued after printing. This was to prevent the need for supports, allowing everything to print flat on the bed. (EDIT: Originally listed as 2.5x3.5in. It has been corrected to 2.25x3.5in)