Watch List notes:

German States, Regensburg. 1745-1765. Gold 1/2 ducat (17 mm, 1.67 g, 6 h). Trade coinage. ND. Crossed keys, R above, B below / Imperial eagle. KM 328; FR 2540. EF, solder expertly removed. Appears to have been a necklace pendant at one point.

From the Larry Adams Collection.

Cf. https://www.acsearch.info/search.html?id=2662098