A continuation of H. B. Gordon's series on microscopic identification of textile fibers, covering the hair fibers with a focus on sheep's wool. It discusses variation in fiber diameter in wool compared with camel hair, cashmere and llama, how to judge wool fineness under the microscope, and kemps (opaque medullated fibers). It also explains the limits of identifying re-worked wool (shoddy), illustrated with 125x micrographs of fine, medium, coarse and re-worked wool. Ends with references and a note that the series continues.