A tubular fitting for medical fluid lines comprising a hollow body (1) within which a male connector (2) and an opposite female connector (3) are coaxially housed. The male connector (2) is coupled in rotation with respect to the body (1) in the direction (F) corresponding to the screwing with a female connector of the line, while it is normally freely rotatable in the unscrewing direction, in the same way as the female connector (3) is coupled in rotation with respect to the body (1) in the direction (G) corresponding to the screwing with a male connector of the line, while it is normally freely rotatable in the unscrewing direction. The male connector (2) and/or the female connector (3) can possibly be locked in rotation with respect to the body (1) in the unscrewing direction, only following a positive command.
