15x15mm junction 2 axis for square / round tubes

15x15 mm system for square / round tubes from DIY store

Inside Dimension = 15.5 * 15.5 mm
Nut Size M5
Nut internally

Easily printable, very stable
0.8 mm shell and 25% filling enough

For aluminum hollow section profile is the weak point.
Tighten the screw only slightly.