You ask a good question about Diggers. I have been slowly doing research on them and plan to do an article for C.O.C.A. I bought Dick Bueschel's arcade library and in it there's a lot of info on the subject.
The Digger, Claw, or Crane machine was a very important and successful product line but for only about 10 years. It began in the early 1920's but took off in the late 20's. It helped that Exhibit and Mutoscope obtained legal rulings in NYC that it was a skill game and not gambling. But it was really a gambling machine. In places where gambling was legal, diggers weren't very popular.
I have found about 12 different makers so far that made many dozens of models.
If anyone is looking to date their digger just let me know.
Ken Rubin
DropCoinHere@aol.com