That's a cool one. When I was a kid we would always look for the green/blue and clear ones that screwed down on the wooden pegs. Thought we were gonna get rich.... Seems like the suckers are everywhere.....
Tom, my brother and I took a serious whipping for shooting some of those off the only power line that ran to the back of the farm.
That power line ran all the well pumps, and the lights in the barn at the back of the farm. 2.5 miles from the county road.
I still maintain I didn't do it, but caught it for not stopping my kid brother.
Here is some like the OP has. Says they are Radio Strain Insulators. Some colored insulators like kc65 mentioned on other pages. I've got a few of the threaded ones like you would see on poles by the railroad. Mine are Brookfield, Hemingray, and Whitall Tatum.