This has four CD 100.5 Pyrex insulators on it. I suspect the threads fit the CD 100.6 Hemingray pieces too. I don't know how it is used.
This is not a transposition bracket. I actually saw these 100.5's in use, on the brackets, on an old toll line over Pacheco Pass near Los Banos, Calif. They were used as [id:451944118; "spacers"] to separate the wires over long spans, in this case, crossing a highway.