At first I made the jaws open wide...
...but they didn't close all the way.
This happened because the movement of the pistons in the small
pneumatic cylinders is not 2 studs as I had thought but a little less.
I had to move the hinge points of the cylinders for ½ studs.
The jaws don't open the whole 90 degrees any more but so is the
case with the real one too.
I found these pictures from the net. If they are yours and you
don't want them to be here just e-mail me and I'll take them away.