Nordic softwood grading rules / Blue book

• The main grades are A, B, C and D.
• Grade A, the highest quality, is divided into subgrades A1 to A4.
• Grades B, C and D are not divided

GRADE A (old classification I to IV or choice U/S unsorted)	Knots	Shakes	Wane	Other imperfections
GRADE A1 (old classification I)	Small sound or dead knots < 7 mm are not considered. Tolerance of 1 intergrown knot per side with a diameter up to 8 mm. Knots clusters, through or dead, are not permitted.	Not admitted	Excluded	Warp must not exceed 2% of the piece's width. Slope of grain must not exceed 1 cm per 15 cm of length.
GRADE A2 (old classification II)	Tolerance of 2 sound knots per side and 1 per edge. The size of these knots must not exceed 25 mm per 75 mm of thickness and 225 mm of width. 1 dead knot is admitted with a size of 70% of the permitted sound knots. All other types of knots (clusters, barkringed, unsound) are excluded.	Not admitted	Excluded	Warp must not exceed 2% of the piece's width. Slope of grain must not exceed 1 cm per 15 cm of length. Gum pocket of 20 mm is tolerated on the poorest meter
GRADE A3 (old classification III)	3 sound knots per side and one per edge. The size of these knots must not exceed 35 mm per 75 mm of thickness and 225 mm of width. 1 barkringed knot is admitted with a size of 50% of the permitted sound knots.	Tolerated on 5 % of the length of a piece with 25 mm of thickness	Excluded	Warp must not exceed 2% of the piece's width. Slope of grain must not exceed 1 cm per 12 cm of length. Gum pocket of 40 mm is tolerated on the poorest meter
GRADE A4 (old classification IV)	4 sound knots per side and 2 per edge. The size of these knots must not exceed 45 mm per 75 mm of thickness and 225 mm of width. 2 barkringed knots are admitted on the side and 1 on the edge, with a size of 50% of the permitted sound knots.	Tolerated on 15 % of the length of a piece with 25 mm of thickness	Tolerated if the length does not exceed 30% of the piece.	2 gum pockets of 50 mm on the poorest meter - bark pockets of 100 mm. Slope of grain must not exceed 1 cm per 10 cm of length - split end of 10% of the piece's width - lightwood equal to 5% of the piece's volume.

GRADE B (old classification V)	Knots	Shakes	Wane	Other imperfections
	5 sound knots per side and 3 per edge. The size of these knots must not exceed 60 mm per 75 mm of thickness and 225 mm of width. 3 knot clusters, dead, barkringed or unsound knots are admitted on the edge, with a size of 70% of the permitted sound knots.	Tolerated per 25 % of the length of a piece with 25 mm of thickness	Tolerated if the length does not exceed 40% of the piece.	2 gum pockets of 100 mm on the poorest meter - bark pockets of 200 mm. Slope of grain must not exceed 1 cm per 10 cm of length - split end of 30% of the piece's width - light wood equal to 30% of the piece's volume - blue and water stains and dote equal to 30% of the piece's volume.

GRADE AB or Saw-Falling (S/F)

Mix of grades A and B

GRADE C (old classification VI)	Knots	Shakes	Wane	Other imperfections
	6 sound knots per side and 4 per edge. The size of these knots must not exceed 75 mm per 75 mm of thickness and 225 mm of width. 4 knot clusters, dead, barkringed or unsound knots are admitted on the edge, with a size of 90% of the permitted sound knots.	Tolerated per 70 % of the length of a piece with 25 mm of thickness	Tolerated if the length does not exceed 50% of the piece.	2 gum pockets of 150 mm on the poorest meter - bark pockets of 300 mm. Slope of grain must not exceed 1 cm per 2 cm of length - split end of 50% of the piece's width - light wood equal to 70% of the piece's volume - blue and water stains and dote equal to 30% of the piece's volume.

GRADE D (old classification VII)

Not used for exports - not described in this document.

Reference:
Nordic Timber Council (http://www.nordictimber.org/)