These stump me. They measure 1 1/2" x 1 1/2" and appear to be cemented (or attached with sulfur) on the pin. There are tiny cracks inside the pieces which make them appear dry process.

The cobalt blue glaze would lead me to believe these are from the U.S. as I don't recall ever seeing a piece of foreign porcelain in this color.

Update: I found other postings which identify these as electric fence or possibly tree insulators.