Here are two that are not listed in GIFONA: The left is a Pre-Revolution Russian insulator, with drip points, made in 1916. The other one is an Isorex DC-16. This may be a CD 251.7, as it has the same dimensions as another listed piece.. I'll show the DC-16 alongside a CD 250.2 for size / shape comparison in another photo. The Russian piece has recently been assigned as CD 589, to the best of my knowledge. Its embossing (in Cyrillic) is Ts. V. - P.K. 1916 // L.O. and is the same one shown here: [id=131827134] Neither piece is currently available for sale or trade.

[IFONA CD 589 251.7?]