Maybe a U-15 or maybe a U-14A? It is dry process, nice and crude and has character. This insulator was used in Detroit on the old Police/Fire communication lines, these are tough to find, 95% of what was used here is Square D, I've only found 3 of this type over the years. There's an old chip on the base, soot filled and about 3/4 long along with another flake on the bottom and a nick on the wire groove. Asking $25 and $9 for shipping.