This is a Namabn tsuba made from a Spanish rapier small sword guard. It is iron and decorated with gold leaf. This is a double lobed "cup" design. Such a piece conjurers up interesting questions and observations. The original soldier that owned this guard traveled a great distance around the Momoyama period to Japan. The Japanese person to have this modified for use on a Nihonto must have had some connection to the trade industry or been a person of means who wanted to display their reach and knowledge of foreign cultures. This is the kind of item that one can get lost in thinking about the things it has seen over the centuries.
Overall the guard is in good condition. There is some corrosion that has left small holes in the plate in one area (see photos). In comparison to "found" examples of old European guards, this one is quite superior.
This tsuba was published in the 9th Kokusai Tosogu Kai book in an article on Namban tsuba by Fred Geyer. Please see the photos of the book and pages below.
It is accompanied by a custom made double box. The outer box is fitted to the inner one and secured with traditional sanada-himo. This is a fascinating piece and an important example in the study of Japanese / European cultural exchange.