Silver stocks found here http://www.cmegroup.com/trading/energy-metals/files/Silver_Stocks.xls
Eligible and Registered Silver
The eligible silver stocks and that of the daily metal warehouse statistics are limited to silver bars that meet the Exchange's criteria for delivery. This criteria specifies that a silver bar must weigh 1,000 troy ounces, plus or minus 10% and be on the Exchange's Official List of Approved Refiners and Brands for silver. The eligible stocks denoted here, and in the daily warehouse statistics, do not include such items as 100 troy ounce silver bars or silver coins.
Specifically, eligible metal is not the same as registered metal. Registered metal is defined as metal which meets the standards for delivery as stated in the COMEX Rules and for which a COMEX Depository Receipt (Warrant) has been issued. Eligible metal is defined as metal which meets the standards for delivery as stated in the COMEX Rules and for which no COMEX Depository Receipt (Warrant) has been issued.
In order for eligible metal to become registered metal, the owner of the metal must have an Exchange Licensed Depository issue a Depository Receipt (Warrant) on those silver bars meeting Exchange standards comprising 5,000 troy ounces (plus or minus 6%) stored at its facility.