A catheter includes a tube formed of plastic, a helical spring coil formed of metal and a ribbon which is longitudinally substantially non­-extendable. The coil is coaxially disposed within the tube and substantially coextensive longitudinally with the tube. The ribbon is disposed within the coil, proximal ends of the ribbon and the coil being secured together, and the ribbon distal end being secured to the coil body at a predetermined point of the coil body adjacent but substantially proximally spaced from the coil distal end. The ribbon precludes substantial longitudinal extension of the coil body intermediate the coil proximal end and the predetermined point, thereby to limit longitudinal extension and increase the pull strength of the catheter.