Chain And Handcuffs (Shackles)

Chain is made of separate chain links. I made three different chain link types:
- with circular cross-section (needs support material )
- with octagonal cross-section (does not need support material)
- with square cross-section with rounded sides (does not need support material. I prefer this type.)
Each chain link has X-shaped slot in the middle. These slots make it possible to interlink chain links into a chain. But it is also almost impossible for chain links to separate on their own. The same method is used to lock handcuffs.

I also made normal sized version for hands and smaller sized version for fingers.
Normal sized version uses M4x35mm bolt and lock-nut to assemble the handcuffs.
Small sized version uses 1.75mm filament (length about 18mm). Then you have to heat up the ends and squish them. I have used heated bed at 120°C, but you can also try other methods (soldering iron, 3d pen, hot water,...)
I have also included Fusion360 files, so anyone can change and adjust