미국 NHLA(National Hardwood Lumber Association)에서 채택하고 있는 하드우드 제재목 등급 판정법을 소개한다. (자료 출처 : Wood Handbook)
In these rules, the grade of a piece of hardwood lumber is determined by the proportion of a piece that can be cut into a certain number of smaller pieces of material, commonly called cuttings, which are generally clear on one side, have the reverse face sound, and are not smaller than a specified size.
The best grade in the Factory lumber category is termed FAS (Firsts and Seconds). The second grade is F1F (FAS one face). The third grade is Selects, which is followed by No. 1 Common, No. 2A Common, No. 2B Common, No. 3A Common, No. 3B Common, and Sound Wormy. Except for F1F and Selects, the poorer side of a piece is inspected for grade assignment.
Source: 『Wood Handbook』, USDA Forest Service, Forest Products Laboratory