What type of key is this?

I'm not too sure what kind of key this is. I purchased it at an Antique Shop. I was instantly drawn to it because of its ornate style. The vendor happened to be there and told me it was a clock key. I brought it home and took a closer look at it. I noticed it didn't quite look like any clock key I have ever come across. Specifically the fact that the inside was threaded. Like maybe it's missing a piece. Does anyone know what kind of key this is? I appreciate any information.