A derivative of the above thing, further parametrized - i.e.

• you can flip the head, the legs, and both arms
• you can set a custom tolerance to allow the prints to interlock properly

Edit the scad file to your needs, export to STL, print.
You may particularly want to reduce the arm length if you decide to print a both-arms-inside-bot.

Two example STLs with a tolerance of 0.3mm are provided, one of which you can connect to infinite chains (or plains, even!)