Jingles is correct however, I think we can nail it to 96 or early 97 because the 640-2 was Reintroduced in .38 special in 97. The next change was the introduction of the internal key lock on the .357 Mag. in 2003 as change 640-3. I'm sure someone more knowledgeable than us will come in to confirm our data or add new data to what Jingles and I have said.