This is a CD 158.9 with the inner skirt embossed "Boston Bottle Works - Patent Applied For - " in a rich deep blue color which is different than the typical aqua color found on most Boston's. A carbon bubble in the glass provides character. This insulator was found on the Central of Georgia Railway line in the late 1960's. At that time, it was the very first of the Boston "screw-tops" documented. It was found on the top tier of a four arm telegraph pole located on the West side of the railway right-away probably a mile or so North of Byron, GA. It came off the fourth pole South of the I-75 underpass.
It is the 4-segmented and was found on a threaded peg with old rusted iron heavy wire which was cut on each side of the insulator. I also found another CD 158.9 in light celery green about 300 yard further South close to a peach orchard near a tank farm. The blue one was kept because the inner skirt has perfect embossing and the other did not. The light green one was trade to a person in New York for a CD 110 Nat. Insulator Co. The light green one has passed through several hands, but was reunited with it's blue brother at the Allentown, PA show in the mid- 1990's ( see http://www.insulators.info/shows/reports/photos/97nia13.htm for Kevin Lawless' Boston Display for more information about Boston Bottle Works.