Contract months are identified by a month code abbreviation which identifies the month in which a futures contract expires. Also called the delivery month.
As an example Silver Futures trade five contracts per year (Mar, May, Jul, Sep, Dec). Using the month codes, the symbol for March is “H” (“K” for May, “N” or July, “U” for September, and “Z” for December). To define the specific symbol, combine the commodity symbol (SI) with the month code (H) for “SIH”.
To refer to a specific year for the March Silver contract, simply add the year. SIH11 then referes to the March, 2011 contract.
The first column is the symbol for the first year while the second column is the symbol for the second year.