This photo is of a CD 247.5 insulator manufactured by Yuznouralskaya Insulator Company in Russia, I believe the plant is/ (or was) located near Magnitogorsk. I got this one from Pavel Yelkin last year.

Embossing reads: ШС 10 A (UFO) 1979

The URL for the "Yuznouralskaya Insulator Company" is here:

http://uik.ru/ru/3.ptid_58.html

However, it is all in Russian, and far beyond my limited knowledge of the language.

[IFONA CD 247.5]