This clamp joins OpenBeam/Misumi 1515 extrusions at a 90 degree angle.
It is meant for axial and radial loads, it will probably not do a good job for angular loads.
The screws (M3 12mm) are off-center by design for two reasons:
1) Make it as small as possible
2) Prevent stress/cracks along the center
Additional parts needed:
Recommended mounting: 4x M3 12mm
Alternative mounting: 2x M3 12mm and 1x M3 8mm
I enjoy designing minimalist-functional 3D objects.