CD 186.2
HEMINGRAY
[010] (F-Skirt) HEMINGRAY-19/[Number and dots] (R-Skirt) MADE IN U.S.A./[Number] {A six sided nut with machine threading is embedded in the dome} SBClear . . . . . . . . . . . . . . $600-700
Another strange style nick named "The Nut". There is a six sided machine nut with fine threading in the dome, and a metal thimble in the pinhole, with perhaps 1/4" space between the two. An ex-Hemingray employee has a machine drawing of this piece, and it is labeled "Spark Gap Asserter". Nothing more. Given that description and the contruction of this insulator, my guess is some device which held the conductor was screwed into the nut. The insulator, with it's metal thimble, was mounted on a grounded pin. As I mentioned, there is a 1/4" gap between the nut and the thimble. Perhaps when excessive voltage was flowing through the wire, it would arc down to ground, and protect some device? Yout decide from the name of the piece and it's construction.