[philso]

You can assemble these with the contacts in various orientations (--, -|, ||,...) so that you can have "special circuits" that can not be plugged into other circuits. I don't recall how many combinations can be achieved so just play with the housings when you get them.

It will take a fair amount of force to un-mate the housings. You can also use a small screwdriver to disengage the retaining tongue and remove the contact from the housing, allowing the housings to be reused.