Baby barrier pressure-mount

This holds a wooden board in the doorway. An adult can step over it, but the kid can't. (No guarantees, of course.)

Print four copies, one for each corner. For each copy you'll also need:

• 2 M3 flat-head screws (length depends on the thickness of your board);
• M10 hex-head bolt;
• M10 nut;
• a felt sticker to protect the door frame.

Mark hole positions in the board, pre-drill with a thin bit, screw the thing in. When all 4 corners are on, put in the bolts in, put the board in place and tighten.

An extra “head” could also fit over the nut for easier tightening by hand; I ended up tightening the bare nut with a wrench instead.

Source: https://github.com/encukou/3d/tree/master/barrier-pressure-mount