Prime grade wooden floors are considered to be very clean in appearance with very few knots and much less colour variation than the lower grades of wood. Any knots will be strictly limited to pin knots and the occasional knot up to 12mm. Prime grade wooden floors do not contain sapwood.
Classic grade wooden floors will have more character than prime grade wooden floors. They can contain sound and cracked knots up to 35mm in diameter and dead knots, which will be filled, up to 15mm in diameter. Again, this grade contains no sap wood.
Rustic grade wooden floors are full of character, colour variation and knots. They may contain sound and cracked knots up to 60mm in diameter and dead knots, which will be filled, up to 25mm. Rustic grade wooden floors will also contain lighter sap wood on up to one third of the plank as well as some limited bark pockets.