Abstract: Method and apparatus for making hollow catheter tubes or tubing from silicone rubber in which silicone rubber X-ray opaque flexible thread is introduced into a wall of the tubing during the extrusion of the tubing. The flexible thread enters the extruded silicone rubber in the extruding die close to the outer diameter of the tube at a line where the extruded silicone material changes from a varying to a constant cross-section. The apparatus is constructed to locate the terminating forward end of the tube through which the silicone thread passes at a line at the entrance to the constant cross-sectional area. The extruded tubing with the thread in one wall thereof is then cured into a final product.