I've removed the metal and glass horn to show the wooden block. I tried to show the threading inside the block. The metal case has threading on its exterior, and the wood has matching threading. Over the years the wood has dried out, making the once tight fit a bit loose. The wood has rings, and that is what you can see in the five o'clock to six o'clock position below the hole. That area is not threaded. Note too, the original red paint on the exterior up at the upper left.