Hello Michael,

Many thanks for the pictures of the Zischang safety, it's had me scratching my head for some time. Now I've seen the drawings, I'm even more puzzled. I'll have to have a think about this one. A two pipe problem Watson.

This may be just a shot in the dark, but the centre pin locating the cam plates goes into a hole that allows precise location of the cam plates, but, if replaced by a screw then these plates have a little leeway in movement which would allow a tiny bit of juggling about of the cam plates. Perhaps it was an easy way of getting the two cam plates into precise adjustment.
Just a thought.

Harry

Biology is the only science where multiplication can be achieved by division.