Corner Piece 3 way with 23mm openings on 2 sides, and 20 mm for v slot on top.
This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/8rbSHlAe5jQ
This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/8rbSHlAe5jQ