Oak frieze class AB
Quality: Occasional healthy knots up to 5 mm are allowed on side A. Healthy knots up to 10 mm, black knots up to 5 mm, and sapwood up to half the thickness from side A are allowed. On the sides, healthy knots up to 20 mm, black knots up to 10 mm, diseased knots up to 5 mm and shallow bark knots up to 30 mm are allowed. These defects must be within 15 mm from the edge. Other defects are unacceptable.

Oak frieze class BC
Quality: Healthy knots up to 20 mm, black and diseased knots up to 5 mm are allowed on side B. Knots up to 15 mm from the edge. White without limits. On side C, healthy knots up to 20 mm, black knots, tobacco knots up to 15 mm, diseased knots up to 10 mm, small bark up to 10 mm are allowed. On the sides, healthy knots up to 20 mm, black knots up to 10 mm, diseased knots up to 5 mm and shallow bark knots up to 30 mm are allowed. These defects must be within 15 mm from the edge. Other defects are unacceptable.