Notched joint.
Notch thru 1/2 each board, wide enough to fit the width of the board.
Imagine your hands as the work pieces...
Make each into a Vulcan salute (open palm, split your fingers - pointer & middle <notch> ring pinky.)
Now put your hands together, joining those notches
I understand what you use the "O's" for,,,
This is my “I plowed snow all afternoon on an open cockpit tractor” face.
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