A guide wire assembly for medical use includes at least a portion which is formed of a plurality of inter-cooperating elements forming a flexible section of the guide wire assembly, and specifically a section that can have varying flexibility. A control device passes through a lumen extending for the whole length of the guide wire and is typically fixed at a distal end of the assembly. The control device is used to change the flexibility of the guidewire assembly and in some embodiments to lock it in position. The elements have tapering internal lumens for accommodating the control device, particularly when the guide wire is bent.
