A device for transmitting rotational movement comprising a flexible shaft having a sinuous sleeve

The device has a flexible shaft (2) and a duct (3) inside which the shaft is placed. The duct is formed of a hollow body made of plastic material and has an inner diameter to permit rotation of the shaft inside the duct. A wall of the body has a variable thickness such that an inner surface (4) of the duct comprises corrugations (6) extending longitudinally over a portion of the duct. An independent claim is also included for a seat adjuster operating mechanism of a motor vehicle.