The grades are based on the percentage of clear, defect-free wood in the board. With Premium Grade, each piece is individually inspected to ensure premium quality, durability and appearance. Visually, Black Locust is known for its knots, mineral streaks, checks, minor grub holes, and bark insertions. To ensure superior appearances, only the most appealing pieces qualify as Premium Grade. Sound included knots, 3″ in diameter and less, minor mineral streaks and small bark insertions are admitted to highlight characteristics of the Black Locust species. Checks less than 1/12th of the board length are also admitted.