I believe they count the number of wales (ridges) per inch. Â The wider the wale, the fewer the count and vice versa. Â I am not sure how many an inch categorizes as wide, narrow, mid, and so on.
Widewales tend to run 8 to 6 wales per inch. Midwales tend to run 8 to 10, finewales 12 to 24 or more (very generally). Bedford Cord is, I think, a different kind of construction, but I'm not sure. Pinwales are very fine, almost smooth surfaced. Corduroy, a pile fabric like terry cloth, has "floats" that are cut and brushed upwards to create the wales/ribs/ridges/piles. Interesting, Men's Health a year or so ago said corduroy pants make your butt look bigger. Anyone find that true?