Knot – A branch or limb embedded in a tree and cut through in the process of manufacturing. Knots are classified according to occurrence, quality, and size.
In lumber, the size classifications are: Pin knot, one not over ½-inch in diameter; Small, a knot larger then ½-inch but not over ¾-inch; Medium, larger then ¾-inch but not over 1 ½-inch; Large, over 1 ½-inch in diameter.
Encased Knot – A knot whose rings of annual growth are not intergrown with those of the surrounding wood.
Intergrown Knot – A knot whose rings of annual growth are completely intergrown with those of the surrounding wood.
Loose Knot – A knot that is not held firmly in place by growth or position and that cannot be relied upon to remain in place.
Pin Knot – A knot that is not more than ½ inch in diameter.
Sound Knot – A knot that is solid across its face, at least as hard as the surrounding wood, and shows no indication of decay.
Spike Knot – A knot cut approximately parallel to its long axis so that the exposed section is definitely elongated.