Square Tube Connectors / Joints + Plexiglass support

The Joint can be used to connect two or three square aluminium tube with external size 15mm x 15mm.
To Joint three tubes you need three M3 screw (size 30mm) and three M3 nuts. You have to print:
1 piece of Joint-a
3 pieces of Joint-b
3 pieces of Joint-c

You can use GlassSupport-a and GlassSupport-b to close the frame with plexiglass or polycarbonate 2.5mm thick.