Splits shorter than one foot are not covered by this rule. The average diameter of any knot shall not exceed in inches one-third the surface measure of the piece. National Hardwood Lumber Association, Box 34518, Memphis, TN 38148-0518. The easiest of these to apply is size. FAS lumber must be at least 6 inches wide and from 8 to 16 feet long.
Lower grades are narrower and shorter.
The next factor is the minimum size of cuttings allowed. For FAS the cuttings must be at least 4 inches wide by 5 feet long or 3 inches wide by 7 feet long. If the board does not have clear cuttings of at least this size, a lower grade must be considered. Next, only a certain number of cuttings are generally allowed, depending on board size. Last, a certain percent of the board is required to be in clear face cuttings.