https://www.printables.com/de/model/386082-wooden-rack-connecting-pieces

General Information I drew the model in Autodesk Inventor. I can confirm that it holds at least 80kg.

I made the connectors for:

wooden sticks with a 19mm diameter wooden board with 20mm thickness But you can change the dimension as you like.

Assembly Material for assembly Screws Drill Wooden sticks Wooden board

How to assemble Cut the wooden stick to the correct length Prepare the wooden board to your liking. I sanded the wood and applied a oil. Drill a hole through the 3D printed part and the wood to screw in the screws later.

Print settings Material I used PLA but it depends on how and where you want to use the rack. If the rack will be exposed to higher heat, consider using PETG or other higher temperature materials like ABS, ASA, etc.

Slicer Settings 3 perimeters 25% infill no supports raft or brim (if you have adhesion problems)