Twill damasks include a twill-woven ground or pattern. The cover was made from cotton herringbone twill fabric. It is usually woven with a plain weave, twill or herringbone structure. It is sometimes woven with a twill weave. Even-sided twills include foulard or surah, herringbone, houndstooth, serge, sharkskin, and twill flannel. South African Battledress appeared in both khaki wool and tan twill. The M1941 green herringbone twill cloth fatigue uniform featured the same hat. The material, formerly cotton, today is a weave of polyester known as "Certified Navy Twill". Additionally, a fatigue uniform was issued, made of 8.2-ounce heavy cotton herringbone twill (HBT) cloth. Sheer fabrics are seldom made with a twill weave. The cloth is woven in a three-to-one herringbone twill composed of flax fibrils. The strands can interlock with either twill or plain weave. The four main weaves for shirtings are plain weave, oxford, twill and satin. The weave is usually twill or plain. Ribbed grosgrain may be used similarly to twill tape for internal gussets and reinforcements.