These are Supports for cube organizers. Mine is from Ikea, Target sells them too. The back panel/flap they come with is flimsey and these help keep everything sturdy and in place. I've included 1 of each piece (Corner, Center, Edge), print as many as are needed for your project. 

My 3x3 cube needed 4 Corners, 4 Centers, and 8 Edges. I used nails to secure the print to the organizers, nails not included