A component for use as or for incorporation within a medical instrument navigable through body vessels of a human subject is provided. The component includes a tubular portion with an interrupted spiral defined by alternating cut and uncut sections. The sum of the arcuate extents of each bridge section and a cut section adjacent to the bridge section in end-to-end fashion is neither a whole number factor of 360 degrees nor a multiple of 90 degrees; this provides uniform rigidity, flexibility, and stretch resistance in all bending planes. The device further includes multiple sections, the pitch of the spiral varying from section to section in order to vary the sections' flexibilities.