The present invention relates to a mechanism for transmitting rotational motion through a sealed wall without compromising the system's airtightness. The mechanism comprises a shaft inclined with respect to the axis of rotation, about which it rotates, generating a cone whose apex is located at the intersection of the inclined shaft and the axis of rotation. This shaft transmits the rotation from its ends to two elements attached to the driving shaft and the driven shaft, respectively, by means of sliding joints (such as friction bearings or some type of roller bearing). An elastic element (such as an elastic membrane or bellows) covers part of the shaft and part of the wall where the cone's apex is located. This creates a coupling that allows the transmission of rotation and torque without relative rotation between the inclined shaft and the elastic element, thus ensuring airtightness through a sufficiently firm connection.