Don't know about Hoosier, but McCreary used to make at least 3 grades of compounds, the SD series, for soft durometer, MD for medium durometer and HD for Hard Durometer, I bought a couple of HD65's at Dayton's auction one time, to run indoors, and still got em, and only ran one, two different times, and you still can't tell it's been run! When you'd grind it to get the marbles off it, sparks would shower like steel! Bob