A tracheostomy tube (1) has an adjustable flange (2) that can be slid along the tube and locked in the desired position. The flange has a one-piece resilient nut (40) that is threaded on a tubular projection (30) on the flange. The nut has an integral inner sleeve (44) divided into separate fingers (48) the outside of which are engaged by the inside of the tubular projection. The flange is locked in position by screwing the nut onto the projection so that the fingers that are forced inwardly to engage the outside of the tube.