Good Delivery Bars are the type held in reserve by the IMF (International Monetary Fund), governments and central banks and they are used in the world's major stock markets (London, New York, Zürich, Hong Kong, Sydney and Tokyo).
Silver Good Delivery bars must have a minimum fineness of .999/1000 and silver content of 750 to 1,100 troy ounces. It's recommended that they measure 250-350 mm in length and are 110-150 mm wide and 60-100 mm deep.
Gold Good Delivery bars should have a minimum fineness of .995/1000 and gold content of 350-430 troy ounces. They should measure 210-290 mm in length, 55-85 mm in width and 25-45mm in depth.
Both gold and silver Good Delivery Bars are stamped with the refiner's hallmark, serial number, fineness and year of manufacture.
Bars that don’t meet these standards but which are similar in appearance are Non-Good Delivery Bars and should be stamped with the letters NGD.