This one was probably manufactured by Verbano around 1954, with 12 54 under the triangular Verbano marking. . Very clean and shiny olive green glaze, Unipart approx 7" X 5" Used to feed electric power to some Italian railroad lines. Probably 12KV to 15KV rating.(see below)
IThis insulator looks quite similar to this one that Nora Coppo posted in September 2007 : [id=195666281]
Update 17-Jan-2008:: The insulator arrived earlier this week, and it is in absolutely mint condition. Also received a very nice "freebie" with it!
Nora Coppo sent me this information:
The insulator you described has been mfd for 15 kv rating, but this item was used on a 3 kv dc line. Roma - Viterbo Railroad feeding line. Also the other (unmarked) versione has been rescued along this railroad line.