insulator or drainplug?

[Stegner]

Ceramic like an insulator, but shaped differently than I'm used to seeing. Is this an insulator? If so, anyone have a guess as to how it was attached to the fencepost?

 

[clovis97]

If it is a fence insulator, there would have been a steel screw at the bottom of the insulator, going through the hole in the bottom of the porcelain, and could be screwed into the wood fence posts.

 

[clovis97]

Also, you can see the rust caused by the screw in the bottom of the bowl.

 

[lostcauses]

May be an inkwell.