I had always thought of the Hevi-Check as being a colored pencil: either red, blue, or half of each. It turns out there was a graphite version too.
It’s an oversized pencil, and so has a large lead core. I assumed it would probably write something like the Editor pencil or others in the same category, such as the Draughting 314, Raven, Special Black, News, Ebony, etc. Instead it’s more like an American No. 1—more powdery than waxy, and it holds a point for a long time.