Here is a small flattish multipart, i found some of these ona railroad around here. Don't know much about them, one i have is embossed with something like "AMC" or "MFG" and then "15AM'. Looks nice, and we had quite the time finding them, then haulling them out of the weeds they were found in.

I've been told it's a pitsburg piece, with a marking of aug 15 A.M. - very intersting insulator