The utility model provides a chain and interior chain piece thereof, should can limit out a clamping space with a relative chain piece by interior chain piece jointly to contain two montage portions that set up along a longitudinal center line interval, and a connection the connecting portion of montage portion, every montage portion all has a montage hole, and these connecting portion have the past concave recess establishing and have two parallel spaced trough rims of direction of keeping away from this clamping space, and this chain of face contains the several interior chain piece, the outer chain piece of several, and the several concatenates interior chain piece reaches outer chain piece has a central axis's chain axle respectively, all has an axis distance between two adjacent the central axis, the axis distance is 2.39 0.12 with the ratio of a total width of this chain. Let this chain more be fit for using in the variable higher field of hop count by this, improve the smooth and easy nature of variable speed simultaneously.