Grade I

Grade 1 willow is surely the most popular  - everybody wants a grade 1 bat don't they? However it's never quite as simple as that.....
Is there anything better than grade 1?  Well yes, sometimes you will see the word Premium or test grade willow, these are usually the very best of the grade 1 clefts.
For a grade 1 cleft I would expect 6-7 straight grains and a white blade with no marks, fleck, blemishes or knots in playing area, you may get a small amount of brown/heart wood (less than 2cm) down one edge of the bat.
For a premium cleft you would be looking at 8+ straight grains, typically 10 or more, again with an all white blade or slight brown edge. Generally these premium blades are also lighter and offer big profiles on lighter weight bats.

Grade II

Grade 2 bats I would say 6-8 grains, with maybe some slight grain wobble outside of the main hitting area. A white blade or less than 3cm brown wood down one edge. You should expect a few blemishes or insignificant marks outside of the main hitting area.

Grade III

Grade 3 - now we start to get into the mid-range, typically 5 or 6 grains, some blemish is possible and possibly some minor marking anywhere on the bat, some slight grain wobble again anywhere on the blade.

Grade IV

Any number of grains, but rarely less than 4 grains. Upto half the bat may be brown heart wood, fleck, mark, stains and blemishes will be present but nothing too serious in the playing area, grain wobble is likely.

Grade V

Anything goes! Any amount of brown wood, any amount of grains, any type of markings, blemishes and stains. These are sometimes bleached to remove some of the brown colour and markings, but this just improves the cosmetics, it doesn't do anything for the playing characteristics of the blade.