An invention is provided which employs a self-adjusting core section having an outer diameter which essentially matches that, or is larger than that, of the inner diameter of a wire coil, where the self-adjusting core has a vertical slit along the its length to allow the diameter of the core to be adjustable. Bridging the vertical slit are straps secured to the core to determine the core's maximum diameter, and allow the core diameter to be reduced through flexing.