A visual grade of sawn softwood. Basically, you start with a stack of timber, and the stack is sorted visually for the size of knots etc. The first timber to be removed is the ‘Sixths’ which is the lower grade from the stack, next to be removed is the ‘Fifths’ grade of timber. Once all the ‘Sixths’ and ‘Fifths’ have been removed, th... Found on http://www.woodworkersuk.co.uk/blog/carpentry-and-joinery-glossary/carpentr