Offered here, is another update/addition to the mystery of glass legs potentially used as battery rests/battery stands. I spoke to Dwayne Anthony at the 2018 Springfield show, and showed him an example that was for sale on one of the tables. I don't have a picture, but it was the style with the threaded glass end similar to what John De Sousa has previously posted. https://www.insulators.info/pictures/?id=519291117. Terry Drollinger has done a nice job summarizing some of the styles of these legs shown here: https://www.insulators.info/pictures/?id=519592340.
Not long after I spoke with Dwayne, a gentleman brought an entirely different style of leg to the show, and stopped by my table for show & tell. These had made an earlier appearance at the recent WRIC Richfield show, and I was alerted to that fact by Rick Baldwin via e-mail. I felt lucky that I was given an opportunity to examine them at length and take some pictures. Much to my surprise, Shawn Seibert, a fellow ICON member, and the owner of these legs, handed me one as he was leaving the show hall. A great surprise gift. Thank you again Shawn!
Each of the legs has two "insets" located across the diagonal of its top surface. The deeper of the insets is registered to a similar inset in the metal cap, so that the cap can only be installed in one position. The cap rests on the top surface of the glass leg. A set screw is used to tighten a removable rectangular piece of metal that allows for pressure from the set screw without damage to the glass surface. The shallower inset allows for the passage of a larger screw from the top surface of the cap, that captures a movable triangular piece of flat stock metal. My impression of this arrangement is that any type of rectangular flat stock could be clamped down between the four legs to create a table-top of metal, wood, glass, etc. I hope this explanation makes sense, but regardless, the pictures tell a pretty good story.
There is wear on the bottoms of the legs from use, ostensibly from this having been moved across a hard surface. As has been noted in previous posts, this sort of arrangement could have been used to support a battery. I like that idea, though to date, no pictorial evidence of that has surfaced.