Here is a classic glass insulator. This is the embossing (010) with the embossing on the base of the inner skirt: Boston Bottle Works Patent Applied For with the mold line over the dome. Has four segmented threads and a smooth base. The color is a nice bluish aqua. Condition: a shallow pinged area on top of the dome; an upper wire rim chip and a small upper wire rim bruise...this is a small area and a light one; a teeney chip area on upper wire rim; and a base chip ...more to the outside of the base. Books at $1000 to $1250 mint. With the condition I have described I will take $795. Postage within the Continental US included.