I have these six insulators coming to me from Italy, CD 648 MIVA T-5s, and small CD 650 T5-S "spooks" in emerald green and light aqua glass, and their porcelain equivalents. These were used as distribution insulators, in pairs, the "spook" accomodated a fusible link, connected to screw terminals between the "eyes". .

The T-5s are about 6 cm tall, 6 cm diameter at the base, the spooks 8 cm tall, 6 cm diameter at the base.

The T-5 is designated as CD 648 and was used for "low voltage" power distribution. The T5-S (designated as CD 650) "spooks" were used as fuses, in that a thin fusible wire was connected between the "eyes" The Italian name was "portafusibile" which means "fuse holder".

I would SWAG that "low voltage" probably meant 220-240VAC at around 5 amps (I have seen vintage electrical meters which were rated 240VAC / 50Hz, 5A). In the 1920s-1930s, the only electrical usage was generally lighting, radios and fans, heating, cooking, and water heating were normally powered with natural gas.

The larger CD 698 two-part "frogs" had similar service as fusible link holders.

Another possible usage for the "spooks" and "frogs" would be to hold a knife-switch for power disconnect. I've seen these on porcelain "spooks".

The T-5 is nearly the same dimensions as the T-6 "nail knob" insulators, and larger than the smaller sized T-6 bis. The T-6 nail knobs were used to support the indoor wiring. Most of these house and buildings were built LONG before electrical distribution was invented, so some rather unique and creative methods of in-house wiring and power distribution were necessary. No running the wires inside teh walls, as these walls tended to be SOLID!

T-6: [id=184588340]

The description, in Italian, is:

sono andato nel sud Italia, ho preso questi isolatori modello T5. Questi isolatori si trovano solo nel sud Italia. sono molto belli per la forma e per le dimensioni. Il portafusibile (spook) misura cm 8x6 e l'isolatore cm 6x6.

Quelli di vetro sono MIVA T5. questi isolatori erano a coppia (1 isolatore e 1 portafusibile (spook) nella stessa staffa, per portare la corrente nelle case.

MIVA T-5 info from CJOW article :http://www.insulators.info/cjphotos/1997/199706-6.htm