Joe,
That's a beautiful job you did on John's hammer.
I recently added one to his collection myself. I was pushing to get it done before I left to visit John and didn't get good pictures of it.
For those of you asking about how to get such a hammer head, John has them custom made by a machinist. Over the years several different people have made them so there are slightly different variations in the collection.
You might say that the hammer collection is a sort of an invitational thing. John asks engravers around the world to do their work for him. His earliest pieces go back about 50 years and include work by some of the best known gun engravers of the 20th century.
RB