It's a CD 214...and the book value is $1-2 in mint condition. I'm sure someone will be by shortly that can tell you more about what lines they were used on, history, etc.
Armstrong bought out the old Whitall Tatum insulator plant in Millville, New Jersey in 1938, but their insulators didn't bear the name Armstrong until 1946. This one is probably from the 1940s or 1950s. If you can tell us the exact embossing on the back, with all the numbers and dots, we can interpret the date code and tell the exact year the insulator was made.
This is a top-tie telegraph style, used on long-distance telegraph lines and I've typically seen this used along railway lines, usually in congested areas that needed the more secure top tie.
Clear and near-clear insulators made after WW2 generally don't generate a lot of interest from collectors or big price tags, but I think it's still a neat piece of history to enjoy.
Great! The back info tells a bit more of the story. A in a circle was Armstrong's logo.
Each mold had a number assigned to it so they could keep track of it in the factory and identify any problems. 5 would be the mold number.
52 represents the year the mold was made, so that's 1952. They added a dot for each year of production after that, so 52 plus four dots means your insulator was made in 1956.
Sarah, pretty nice insy, I sold a lovely amber example just a few weeks ago on feebay for 15.50. That same week, I sold a cd 230.2 also in amber for 65.00.
These Amstrongs are getting more popular every year. It used to be that you couldn't give them away, but they are coming into their own.
Thanks for posting a very nice photo,
Fred