"Supremus Dux In Prussia 1686"

G'day
"... The Duchy of Prussia remained a largely autonomous vassal of the Polish-Lithuanian Commonwealth until 1657, when the "Great Elector" Frederick William of Brandenburg achieved full sovereignty over the territory in the Treaty of Wehlau, which was conclusively recognized in the Treaty of Oliva (1660).
The personal union is referred to as Brandenburg-Prussia until it was elevated to the status of a kingdom in 1701.
Frederick William (German: Friedrich Wilhelm; February 16, 1620 - April 29, 1688) was the Elector of Brandenburg and the Duke of Prussia from 1640 until his death. He was of the House of Hohenzollern and is popularly known as the Great Elector (Großer Kurfürst) because of his military and political skill. The Great Elector was also a staunch pillar of the Calvinist faith, associated with the rising commercial class. Frederick William saw the importance of trade and promoted it vigorously. ..."
The dates and abbreviations on your coin seem to fit the above narrative.
However, I must say that the coin in the photo looks very primitive: cast, rather than die-struck - perhaps a replica ?
Peter in Oz

Hello,

This coin should have been a silver Brandenburg 6 groschen KM#429, but I agree with Peter: this coin seems to be a crude counterfeit (or, staying friendly, a replica).