Take a common insulator and a worthless old rusty bottle cap, combine them into one and what do you have? A Junkman's prize!
Knowing I have a strong hankering for wild junky glass insulators, a good collector-friend on the opposite coast always contacts me when a good piece becomes available. He said this one was in a crate full of commons that were tossed in with a collection purchase. He didn't even notice the inclusion until he went through the box a second time.
It sure makes a great companion to another recently acquired bottle cap seen here in a star signal: [id=322437465]