NYDigger is correct. These were used from c. 1910 to 1921 by Hemingray until it was replaced by the CD 154 and even more common Hemingray 42.
I got into collecting insulators as a bottle collector too. My father has been a lineman for over 15 years. He took a few blue ones out of service that had been repurposed for power lines when these were usually used for telephone. Those ones are what got me into it.