This is a sliding lock to deter young children from opening bi-fold doors. It simply slides over the hinged area to "lock" the door.
The inside depth of the slider is 30.5mm for a fit on my doors which were around 29mm thick.
Update: It actually works really well.
UPDATE 2/16/18: Added a version without a handle. Can print standing on end without support to increase strength along axis that will receive the most stress.