Most honing steels are slightly magnetic. When you use honing steel on your knife's edge. It can remove small metal particles. Such metal particles might accumulate in the pores of the steel and clog them over time. This can cause the steel to lose its functionality as the pores fill with small metal dust. And the rod becomes sleeker. People frequently believe that their rod is simply wearing out and that they need to replace it. In fact, the flatness of the rod is simply due to their lack of cleaning it after each usage.