It is worth adding to the Wikipedia notes that the Bradford count is not exactly equatable to the micron count. The micron count measures purely the fibre diameter. When wool is spun, it seems to have a 'preferred' thickness of yarn into which it spins most readily, which is dependant on factors additional to the fibre diameter, such as the handle of the wool, number of crimps, lustre etc. The wool workers at Bradford were expressing the overall qualities of the batch, as opposed to the simple average diameter of each fibre