Twin metal billets (31) are fed to dual circumferential grooves (44) formed in a rotary wheel (43), and are advanced to a die (21) which has a die opening with a circumferentially discontinuous, annular cross section. The metal merges in the die opening and exits therefrom in the form of a slit tube (34, 36). The tube is advanced over a forming member (38) to form a flat strip (39). As the tube is advanced over the forming member, an alignment system (300) maintains the tube in a centred position. The alignment system includes a light source (302a, b) disposed within the tube and two arrays of photo-transistors (308) arranged to receive light from the light source, the amount of light sensed by each array being a function of the position of the slit in the tube relative to a desired position. Any difference results in a steering roll (318) in contact with the outer surface of the tube pivoting in a direction which will bring the tube back into alignment.