And Bernard you can unscrew the tops of those insulators, originally there would have been another one on top on the upward arm for open 40cc copper wires and these were then nibbed onto the 2 core black and red lead in.
There are versions of open wire insulators that had removable tops but informed sources ( retired GPO linesmen ) confirm that on the majority of domestic service the insulators were one piece.
Well as a retired ex Gpo linesman (came out of apprentiship in 1974) I can tell you the upper part of the insulator does infact unscrew to enable you to nib the bare copper wire to the lead in (bear in mind there where two bare copper wires seperated by about a 12 inches on the overhead) this enabled you to keep the connection dry.Common in most domestic situations.
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