Its manufacture demonstrates from an industrial aspect a period of history following the occupation of Japan by the USA after the second world war and has a strong association with this event.Insulator - known as an egg type - ceramic - fired clay (porcelain) finished with a brown colour with two holes for span wire with the holes offset to each other. Marked in a very light almost clear finish on one side "Made in Occupied Japan" See item 8534 for another example - a larger size. https://www.gotheborg.com/glossary/occupiedjapan.shtml - accessed 15/4/20201 gives some background: "For the period from the end of World War II in 1945 through April 28, 1952, the United States and its Allies occupied Japan. The Occupation involved approximately 130,000 Americans (both military and civilian) and about 35,000 British Troops based in Japan. SCAP (Supreme Commander for the Allied Powers), led by General MacArthur, wrote a new constitution for Japan. As Japan needed to rebuild their economy after the war, part of the agreement to allow them to export goods out of their country was that they had to mark 50% of all items with "Occupied Japan" or "Made in Occupied Japan." This could be done with a paper label, cloth label (as on scarves, doilies, clothing), engraved, handwritten or stamped. Thus, you may come across things, such as a salt and pepper set, where only one of the pair is marked OJ and the other will just have "Japan" on it. The tags, labels, marks were placed on the items in Japan, before they were exported to other countries. "trams, tramways, overhead, trolley wire, insulation, electrical equipment