Finding and marking the exact center of a small metal rod or dowel is more difficult than finding the center of a larger circle. I recently wanted to mark the center of a 1" long x 3/8" diameter brass rod, then drill a 1/8" concentric hole the entire length. Yes, just a brass rod with a hole down the center. A professional machinist with a metal working lathe might have no problem with this, but for the average garage shop guy (me) it was no easy task. I learned a few tricks and made a jig that made the job easier and the results better.
With apologies to my friends in metric countries (everybody except U.S.), my example is in Imperial units. Everything applies to S.I. components and drill bits.