An apparatus and method for providing a co-extruded, tapered multi-layer shaft. The stretching property of the stretchable cloth forming an upper part and the stretching property of the stretchable cloth forming a lower part of the internal structure are differentiated from one another so as to be smaller in the latter than in the former. An API library is a set of commands and functions that can be used when developing a navigation program and a set of protocols defining procedures.