The idea with the breastsqueezer is similar to that of
a nutcracker. The intended pressure is of course less to the one cracking a nut,
but anyhow.
The breastsqueezer is made from two halves, made from e.g.. stainless steel,
which are connected at the top. When you pull the (black) line, the two halves
will squeeze the breast at the base, around the screw at the top.
The idea is, that you fit two breastsqueezers on a rim ( e.g. a leather- ) so
you have one around either breast.
When pulling the line, the breast will squeezed at the base, and that's the
whole idea!
It's possible that you'll need to use some kind of padding around the hinge (
"Hængsel") in order to prevent it from 'biting'...