These grading rules are established by NOFMA and apply to American Black Walnut.
This grade of walnut comes in longer board lengths and has natural color variations found in heartwood and steamed dark sapwood. It has an even brown appearance and is almost entirely free of natural imperfections such as knots and pin worm holes. The following characters are admitted: broken knots up 3/8" with no loose pieces; slightly open checks; intermittent machine burn; indentations and slight amount of scant thickness.
This grade of walnut has a more rustic appearance with shorter boards lengths when compared to higher grades. It contains sound, natural variations and manufacturing imperfections. Larger knots (both sound and open), unlimited sapwood, and some checking and worm holes are permitted. All imperfections and open characters must be fillable.