Picked this up out of a pile of old porcelain insulators. I couldn't find anything on it on the web. The markings on the top are "T.R. No. 4.," under the "W" Westinghouse logo. I tried to remove the top metal plate, but it seems to be glued on pretty well. The whole unit weighs about 20 pounds. The widest part is 8 inches.

Another member emailed me and said this could be a type M-2415.