Here is a slotted friction fit faceplate design for 20mm Plastic T-Slot < http://www.thingiverse.com/thing:10261 >. Holes are provided to accommodate M3 bolts either for permanent mounting or to hold in place while framing. As a fully printable hardware system, the holes provide a place to dribble acetone permanently adhering beam to plate. When using bolts take care not to over tighten.Print face up without support. The main failure mode for this piece will be de-lamination of the face to the slot and groove. Printing too fast, too cool, or overcooling can cause this.