I don, t do much porcelain, but this old railway insulator, covered with soot, peaked my interest..Believe this is what they call a dinosaur egg, and fairly old, this is the threaded verison, with a grooved base,,looking to find who produced this, is it Canadian made,(what era)and just how common are these both threaded and threadless, i don, t see any listed for sale, can anyone give me a value of both styles