The OpenBeam L bracket is the most versatile joining bracket in the entire kit. It allows for four joining configurations:

1. The standard 90 degree joint.

2. The 3x90 degree joint, in the corner of a cube. Note that the extrusion is end tapped to allow 3 pieces to be joint together.

3. A 45 degree bracing joint

4. Twin 45 degree braces.

http://blog.openbeamusa.com/2012/05/29/in-depth-the-l-bracket/