A left and a right corner that allows you to use the Maximera drawer without a front board. So you can put a printer in the drawer without it drooping, and still access the control panel and open the door and stuff. 

It's a bit of a pressfit, I printed it in ASA and with 15% and 30% infill, they both work. 
Never used the screws to screw it on, it seems to hold. 

The fusion model has a stick that has a hook that could connect to the wire loop in the drawer - but it always breaks off when tightened. Probably needs a separate part that joins, but it's not necessary for keeping the edges in shape.