An electromechanical surgical system (10), comprising: a surgical instrument (100) including an instrument housing (102) defining a connecting portion (108A) for selectively connecting with a shaft assembly (200), the surgical instrument having at least one rotatable drive member (118,120, 122)； an end effector (400) configured to perform at least one function； and the shaft assembly (200) being arranged for selectively interconnecting the end effector (400) and the surgical device, the shaft assembly including a transmission housing (212) configured and adapted for selective connection to the connecting portion (108a) of the surgical device and to be in operative communication with each of the at least one rotatable drive member (118, 120, 122) of the surgical device； an outer tubular body (210) having a proximal end (210a) supported by the transmission housing (212) and a distal end (210b) configured and adapted for operative connection with the end effector (400)； an articulating neck assembly (230) interconnecting the tubular body (210) and a distal neck housing (236), wherein the articulating neck assembly is configured to enable off-axis articulation of the distal neck housing and wherein the rotatable drive member extends through the articulating neck assembly； the distal neck housing (236) interconnecting a rotatable drive member (118, 120, 122) of the surgical instrument and a rotation receiving member (426) supported in the end effector, wherein the distal neck housing (236) includes a first end that is connectable to the rotatable drive member (118, 120, 122) of the surgical instrument and a second end that is connectable to the rotation receiving member (426) of the end effector, wherein the distal neck housing (236) transmits a rotation of the rotatable drive member of the surgical instrument to the rotation receiving member (426) of the end effector, the distal neck housing including: at least one gear system configured to convert a rotational input of
