springer front fork casting #'s ...

[pete reeves]

Some late 1936s have number 2 so 1937s would almost certainly have 3, I don’t know when 3 changed to 4 but it’s possible some late 37s could be 4.
Pete reeves 860

[Chris Haynes]

This line of thought would have you believing that only one set of tooling was in use at a time.

[pete reeves]

Chris.
There would almost certainly have been some cross over and it’s equally probable that more than one tool was in use at the same time. But it’s very unlikely you will ever find a 1936 with a number higher than 2 on it.
Pete Reeves 860

[silentgreyfello]

1st.... I don't know diddly about knuckles, but I have an early 39EL, so I was interested in this thread and if my fork was correct. My fork has a 7, so I am guessing it was changed out at some point?

I did want to chime in on the forging process, as I have been around it a bit. It doesn't make sense to me that they would run two forge dies at the same time because production was not that high to require it. I would think that they would have put an order in for a new die when the old one started to wear out. When a new one came in, the old one went on a shelf as a backup. A two man crew certainly would have been able to knock out a 100+ parts in a shift with one die, one guy tending the parts in preheat, other running the press. After they were forged, on to a mill for machining, then into a bin, ready for brazing. I suppose a newer version part could be dumped in the bin with the older parts, so I think this is where any mixing would take place. Just a theory, and certainly not based on facts.