I have folding doors in my house, and my cats know how to open them. I needed a way to keep them from doing that, so I created this swinging latch. The rotating part goes on one side of the center hinge, and the eccentric post goes on the other side; measure 13mm from the edge for each. Holes are for US standard #10 screws (regardless of door material, get the panhead type which are probably called "sheet metal screws"), and you must adjust the tightness of the swinging part carefully so it works right. The "post" is eccentric to allow you some room to adjust how tightly the latch works.

If the sides of your door are not precisely even, you may need to add a washer under the swinging latch to aid with clearance.

Updated 4/22/21: I've added a left-hand-side version of the STL and updated the FreeCAD file to include both orientations.

Updated 5/8/21: I identified a weak point in the design and thickened the back side of the hook to compensate.