Mr. Maim and I discussed this at SAR. As I interpret the pertinent chapter in Dolf Vol. I, it appears that production had begun on the 1917 tripods when the desire for the fine, worm gear traverse mechanism was implemented. Production stopped while this was being created and introduced to the casting. Then, it seems the idea did not gain favor so, during the late production period, they stopped putting the mechanism in. If that theory is correct, it explains why there are sockets with the hump and cavity cast in, like on my tripod pictured in the OP, but the finish machining was not done for the worm gear. Then there are those where the mechanism was removed, or at least the pocket had been finish machined, and a freeze plug set up was used to seal the openings. I have a socket like that as well.
What makes a unique find, however, is a socket that has the groove for the traverse stops- as would all WWI 1917 sockets- but does not have the cast in hump. That suggests to me that it is the very early production. The example Mr. Maim found is only the second I have seen like that. Might be the rarest variation.
Of course, the rarest of all is the early cradle, which usually is found only with a very expensive transferable 1917 C&R. Most of those 1917 cradles were scrapped, with replacement by a 1917A1 cradle which was adopted in the mid 30s. So, finding the early lower with the late cradle is normal.
To greaser, I will get with you on the specs. Could use another set or two myself.
