Optical step index fibers can be produced that include a thin metal wire in the centre of the core. Such fibers are particularly interesting with respect to their guiding properties. With the goal to theoretically analyse their modes, we summarize three analytic solutions for dielectric media containing a thin metallic wire. In addition, we present a solution for the most general case of a step index fiber containing a metallic wire with finite conductivity. The analytic solutions serve as model cases which are used to evaluate the accuracy of numerical simulations and to find the most appropriate simulation parameters. Given those, more complex structures can be investigated.