A very unusual brown-glazed JD suspension. It's 12-1/2" in diameter & must have weighed quite a bit. Note the spiral grooves, perhaps meant to carry away rainwater? Also, note the ball-and-socket style hardware, instead of the slots found on most typical blue JD suspensions.
From the book "Porcelain Insulators and How They Grew" by Brent Mills, 1970.