This is a latch for a storage box that will hold it securely closed.
The body encloses a printed hook that engages a post in the lid part.
A knob-and-spindle pass through the body and hook. When the knob is vertical the box is securely latched. The spindle has round and square sections to allow it to turn, but also securely grip the hook.
It can be printed in parts or all together. Size can be customized.
I recommend printing the body at low infill and the hook and spindle at high infill, but printing the whole lot at 25% worked well for me.
Updated 2019-03-24 to fix a bug when rendering just the knob/spindle part.
I designed this to be printable in one piece but have not succeeded in freeing one yet.
If you print the parts separately you can assemble it.
Printing the whole thing at 25% infill works, but you may want to print the hook and spindle at 100% infill.