Thick wool       Turkey 6-ply.
Wilton "6-ply" (really 3-ply).
Herdwick 3-ply.
Medium wool   Mixed thrums (generally Axminster) 2-ply. Fine wool  Brussels thrums (see special description below).
Crewel wool.

The word "thrums" is an old one and it is interesting to read the advice given by an Elizabethan chronicler to a young venturer to the East at the time when new and exciting textiles were being introduced into England: "In Persia you shall finde carpets of course thrummed wooll, the best of the world, and excellently coloured . . . and you must use meanes to learae all the order of the dying of those thrummes, which are so died as neither raine, wine, nor yet vinegar can staine."