These central rotating bodies are applicable to small excavators with an application scope from grade 1.3T to grade 13T. These products are designed to connect hydraulic pipelines of fixed and rotary parts of the whole hydraulic system, making the upper and lower parts of system hydraulic pipeline have 360 relative rotary motions without any intermittence, moreover, two oil port channels are improved for oil cylinder of mould board, realizing all-in-one of digging and earthmoving.