Question of the Day Expires at Midnight, EST (New York)

9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B, and 9xxB, are grades assigned to what common object?

Clues