I will just make a few quick comments as otherwise this thread will become too confusing to follow since the original question was about a 1967 jack only.
Just want to point out that Ford never actually made any of the jacks. They had three vendors doing this, and all three had manufacturing plants in the Detroit area. In the example of the coarse thread jacks these were all manufactured in St. Joseph Michigan and shipped to all three Mustang production plants. And these same three vendors made the jack handles as well. There are variations over the years of the jacks and handles.
As for the date codes, I want to make sure we are not intermixing the first generation jacks, because those are included in the pictures in the previous postings which adds to the confusion. None of those would have date codes. There is a specific reason the date codes started in Jan 1967 which had to do with government regulations. I cant say that every single jack ever manufactured after that date did have one....its likely some did not, just like not all engines got the VIN Numbers stamped that were 'supposed' to. Remember, from '64 to '73, we are talking about 3 million Mustang jacks. Same with the paint process.....there could have been changes made during all those years, but I can make some general comments based on the data I collected and the drawings I have.
I will share everything we have found with detailed pictures when we are finished. Trying to get that done very soon, hopefully in the next month or so.
Jim,
I have no idea what the "double square cut thread" is that you are referring to. If you post a picture it would be useful.