I got this small "liberty bell" shaped insulator at Keene a couple weeks ago. It is believed to be French, it was originally "cemented" onto a small angled metal bracket with white plaster. It is not actually threaded, but has four groups of three small indentations to hold it in place. It is about the same size as a Surge CD 100. I got from Caleb Thimell that it is a CD 528, probably was used in Morocco, manufactured in France, unknown source.

New update: This may be from Algeria, formerly used by the French Foreign Legion for telegraph or telephone service. GIFONA states that there are only a few of these known to exist. I guess I hit the glass lottery that day...

FWIW, this one is also known as the "General Morice Insulator".

[IFONA CD 528]