Marking:

(Embossed around pinhole)
THE M & E Co PHILA. PA / KEYSTONE

Jeff Katchko brought this piece for show and tell to the March 3, 2001 Maryland Line, MD insulator show.  Jeff located it with a metal detector along the Scranton & Moosic Lakes Railroad which was built in 1902 and abandoned in 1907.

Interestingly, this piece has a brass cap that screws onto an iron body.  The composition insulation has started to squeeze out of the iron shell.