An anti-unscrewing device for coupling the tubular ends of two components in fluid conveying or delivery systems by means of a threaded ring nut that can be screwed to one of said tubular ends to connect said ends, wherein said anti-unscrewing device comprises a connecting portion to connect the device to one of the components and at least one counter element provided with an engaging portion suitable to engage a corresponding engaging surface formed at said ring nut, such that the engaging portion can be displaced by means of a movement of the ring nut. There are further provided guide means dictating a movement path for the counter element, such that an unscrewing movement of the ring nut will cause the engaging portion to move to a locking position relative to the ring nut thereby preventing the ring nut from unscrewing.