I am really not sure what these are called but I have seen these used on the top of very large porcelian insulators with some kind of mechanical device inside. Both are etched with the General Electric "GE" in a circle with a band around the perimeter. The purple one is 6" tall, 4 3/8" wide with 1/4" thick glass. The orange amber one is 9" tall, 7 1/2" wide with 1/4" thick glass. The bases are ground on these which apears to be part of the manufacturing process. Other than tiny nibbles along the ground surface area, both are in excellent condition. Price is $40.00 each plus shipping. If someone has a better description or reference as to what these are, please let me know.