Found this in a junk/hoarder's shop near Youngstown, OH. Nice variation in the glaze. Wasn't familiar with this Thomas marking, but Connor Stoehr gave me this information: "This is a very late production Thomas with the Delta Star sandblast marking. In 1957, the Thomas company was sold to the H K Porter, which merged it with their Delta Star Electric division and sold insulators under that name. This continued until 1963 when the Thomas plant was closed for good."