The bed corners are the companion to the 3-point bed support. Like the preivous part, a 4 mm screw hole is available for bed leveling. The corner is open to prevent interference with the glass corner. An M4 x 6 mm set screw is used to provide a leveling adjusment (McMaster PN 91313A139). These are parts I had on hand. I use a 32 mill sheet of FR4/G-10 (McMaster PN 8667K51) under my heater. This provides some thermal insulation, supports, and protects the heater and glass from the set screw stress. Something similar would also work. Demonstration video: http://youtu.be/n6wtOR66uoA EugeneABS printed at 0.2 mm layer height