Rick Soller and others examining this rare Hemingray "battery rest insulator". I understand that this was part of a private transaction, and was passing from seller to buyer at this swap meet. If I recall correctly, there are something like three of these known.

Charlie Irons furnished the following update, which I quote with his permission.

Steve:

I was just looking at your photos of the WINTER BLAHS show on ICON. As a point of information the HEMINGRAY ODDITY that was pictured and thought of as a Battery Rest, an article that was published in the Spring 2014 issue of the NIA Drip Points concludes that there is not enough information to confirm or deny that this is a BATTERY REST. At the time of the article there were 5 known.

Footnote by Steve: Occam's Razor suggests that the simplest explanation is most likely to be the correct one. So here we have an ODDITY that has a cavity on the smaller diameter side, that looks like it ought to fit a pin on the bottom of a battery rack, which would keep the ODDITY from moving relative to the frame it was supporting.

I look forward to further research revealing what this thing really is! Meanwhile, the fact that only five are known probably means that, with regards to price, the sky is the limit!