CD 147 PATENT OCT. 8TH 1907 (Brookfield or Hemingray product)

This interesting insulator was designed to a John Barclay patent to allow replacement of broken insulators without having to replace or remove the tie wire.  The threading would allow a new insulator to attach to the existing tie wire while being screwed onto the pin.  Both Hemingray and Brookfield made these units.  

PATENT OCT. 8TH 1907 (Several variations including one with HEMINGRAY on the other side)

Smooth base -- Aqua