Nice acquisition, Oily. There are more clues there than you can shake a stick at. I am going with 1929 to 1930. I noticed there are many references to the Thorsen Process, but no mention of "Techniheat" which is what they started calling it in 1931 (April, according to AA). Also, Boeing Aeronautics became United around that time, but of course there never is a "day one" on those kinds of changes. The Boeing School of Aeronautics was established in 1929, according to one reference I found, so no earlier than that. I chose the latest date as 1930 because I would think Thorsen would start using the "Techniheat" reference as soon as they came up with it. They had the process, but not the name in your catalog. By 1931, thier literature included the Techniheat name ... but not until April, according to AA. So, oldgoaly is probably more correct with his wider estimate of '29 to '31. But if I were to try to narrow it, I would leave off the 1931.
I also noticed one of the valve grinders was patented in 1928, but the patent had been applied for in 1924. If you tracked down every corporate reference mentioned in that catalog, you'd be making one hell of a contribution to the study of tool manufacturing / marketing during that early era.
As usual, the easiest part to nail down is the "no earlier than" aspect. The "no later than" side of it is far more difficult. I even researched the "Sec.384 1/2 P.L. & R." reference on the front cover. No joy there, as that is a reference to a Postal Law and Regulation citation which first appeared in the 1870s. What I could not find, was when the "1/2" was added to Section 384. If one could find out when Section 384 was ammended, it may help to narrow down the "no earlier than" side. I also looked at the alpha-numeric phone numbers on the cover but that was no help either. The transition from alpha-numeric phone numbers to all digital was a controversial battle which drug out all through the '50s and into the '60s ... so, no clues there either.
I often wonder how difficult it would be to track down the artists that created the work on these early advertising pieces. I have tried to contact the "Poster Expert" on the Antiques Roadshow to see if he could provide clues to the artist(s) that created some of the great art found on the Proto ephemera and others, but he did not see fit to reply to my query. If such information could be found, there would be another avenue of exploration. The artwork on your flyer is pretty distinctive and the originals are probably hanging in someone's living room. And, no doubt, their significance is slowly being forgotten. Judging by the similarity in styles, it may have been a small group of "go to" guys that created all of that tool art. Possibly even a single agency with which they were all involved. I may try to contact the Roadshow guy again. I think he may know who created some of the art.
