Tower Bow Lock Cuffs

In my collection of Tower Cuffs I came across a pair with the patent date of December 5,1882. This is the patent date of the addition of the bow lock. This set has no bow lock, however it does have a hole in the top of each case where a pin could be inserted to prevent the bows from closing. The only other markings is a "D" stamped on the body of each cuff. Maybe this is in reference to a cell block.

The holes may be factory made (they are well done) or some person thought this might solve the problem to keep the cuffs open. Anyway it seemed interesting with the patent date.

Ron