This is a nice Blue-Aqua CD 105 base embossed "American Insulator Co. Pat. Sept 13 1881" which eight lines over the dome - it is a three piece mold. A half a dozen of these were found on the Central Georgia Railway line between Macon, GA and Albany, NY during the late 1960's. This is the only one that was half way decent. I also found a damaged "doted" line dome variety. I again speculate that these must have been cheap replacement insulators since one would expect these on a early telephone line and not on an old telegraph line.