The Russell 2000 index is the key to this year's trades, he told viewers of his "Mad Money" TV show Thursday. When a company gets added to the index, the biggest advantage is that the stock gets a lot more attention and promotion, Cramer said. Every year, the Russell indexes (not indices), he explained, need to be rebalanced because of certain stipulations the indexes have. The annual rebalancing of the Russell 2000 index, which is made up of 2000 small-cap stocks, will take place in June this year. To be eligible for the Russell, which makes up its own rules, a stock must have a market capitalization of $233 million to $3 billion, trade on a major exchange and trade at more than $1, among other conditions, Cramer said. On June 22, the Russell 2000 will be reconstituted, and all companies that don't meet the criteria will be "purged and replaced," Cramer said. "The additions and deletions are based on stock prices as of today's close."