[Taylor]

Here's another (emphasis mine):

2 - While we understand that "hard" is a relative term, we do not define a specific hardness rating (understand that many teams and inspection stations do not have the tools required to measure specific hardness). Hardness is used in the general sense of the word as understood by a reasonably astute observer. A rule of thumb: If I hit you with it and it hurts, then it is "hard."