The invention discloses a single-number chain which is a ring body formed by connecting a plurality of chain links in series. The front end of one of every two adjacent chain links is connected with the rear end of the other one of the two adjacent chain links in a free rotating manner, each chain link comprises chain pieces, protrusions fixed to the chain pieces and a pin shaft for fixing the twochain pieces and the two protrusions together, protrusion holes are formed in the protrusions, chain piece holes are formed in the chain pieces, and transmission of the single-number chain can be achieved by fixing the chain pieces and the protrusions together; the number of the chain links of the single-number chain is a single number, the single-number chain can be matched with a frame in any size, and the problems that as for an even-number chain, the requirement for the number exists, the number must be an even number, or the phenomenon that the chain is too long if one chain link is increased and the chain is too short if one chain link is decreased when the error value of a rack is too large sometimes are solved.