This is a brass coin weight dated 1842 that was used for checking the weight of a British sovereign gold coin.  The weight would be used with a balance scale, the brass coin weight being placed on one side of the scale and the actual coin on the other side.  This coin weight is listed in the Withers British coin weight book as #2270a.  Guaranteed genuine.  Please also see my other eBay coin weight listings.  Free shipping in the USA.