The piece shown is the adjustment bolt for a common Dahon frame latch. IIRC these were called "Vise-Grip", not "LockJaw".
The larger threaded end screws into a cylindrical piece that rotates in the frame latch. The thread is M6-1.00.
The threads at the other end are the remains of a screw that connects the adjusting bolt to another cylindrical piece that is mounted in the frame. This screw has a M4-.70 thread and is long enough to bottom out in the hole on the adjustment bolt without binding the cylindrical piece; this connection is supposed to be loose so the adjustment bolt can rotate freely.
It's not clear why the head of that screw broke off. Possibly it unscrewed to the point that the head was interfering with the operation of the latch. In any case, you should remove the remnant of the screw and replace it. I'd try grabbing it with pliers, or clamp it in a vise. You can probably find a replacement at a good hardware store (get stainless steel). Adjust the length so the screw *almost* binds the cylindrical frame piece.
If you want to go "official",
THIS looks like it might be the same latch.
There is a thread describing a similar problem to yours
HERE.
This is from another Dahon frame latch. The screw inserted on the right is bottomed out in the hole.
Here's the screw out of the hole. It's about 13mm long. So, basically you just need this screw!
Hope this helps.