Thanks Hondo44, my studies are only beginning. I have not fitted the side plate to the frame, as yet. I only have access to the standard 1917 hand without hammer block. I will take measurements, as suggested, and get back to you. The trigger and cylinder stop assembly function well without the hand. With the hand installed in the trigger slots it sticks 2/3 way thru its cycle towards the end of its travel in the frame cutout Is the hammer block hand thicker at its base than the non-safety hand? It seems to ride high on the trigger.