Take thread continuity and thread continuity as examples. The continuous contract here does not refer to a specific contract, but changes, mainly for the convenience of observation and research. The current delivery month of snail is 1004 contract, and "thread continuity" is the first trading contract after the current delivery, namely 1005. "Threaded three-in-one" is the third trading contract after the current delivery, that is, Threads 1007, other varieties, even three and four, and so on.