The medium 9 variety is an interesting one. The bottom of the 9 is higher than regular and points at the base of 2, so some people confuse it with High 9, but the top of the 9 is aligned unlike the High 9. That's because the last 9 is smaller than the first one (~1.0mm vs ~1.1mm). I think "Small 9" would be a more accurate name for that variety.