People did not buy new cars every couple years during the 1940s and 1950s, so worn GM keys were a normal occurrence. All GM code cuts in the 8000-9499 series add up to an even number. Every GM key that came into our lock shop during those years was read by eye and then an original key was cut using the GM stamp machine. It was faster than duplicating and every customer left with a more exacting key than the one brought in for duplication.
For locksmiths who wanted to make sure they were cutting the correct key, Briggs & Stratton also made a key reader. The key was simply inserted into the housing. Cuts on the key pushed tumbler indicators into position and cut depths could be read by seeing which depth bar the tumblers aligned with. Any locksmith worth his pay could quickly figure out the four depths by eye so this tool got little usage in our shop.
It was a sad day in 1967 when GM brought out the 6-cut, 5 depth keys with new keyways. Our little GM key cutter could not cut the new "5" depth and it gradually got less usage. The Briggs & Stratton tool in these pictures is the same machine that this reporter used to make thousands of GM keys during the good old days of the 1960s!