These are brackets meant to support a piece of plexiglass on the front of an Ultimaker 2. The brackets hook over the front edge of the case, and hold a piece of plexi quite firmly. The brackets are mirror images, and meant to approximate the curve on an Ultimaker's front panel. These were designed to avoid having to unscrew portions of the Ultimaker's case when adding a door.Print at a high enough infill to be sturdy - something like 30% at least. Mine are made from ABS.