Leather Cowhide or horsehide may be used for reinforcing patches where heavy wear occurs. It is used for reinforcing patches for grommets and chafing strips on seat belts. Artificial leather has replaced the natural product, and is used to a large extent for seat pad, crash pad, and upholstery covering. Vinyl Vinyl is a plastic material and is used in many instances in the fabric shop. Vinyl is available in various thicknesses, depending on its intended use. It may be used for seat covers or ventilating clothing. The type used for ventilating clothing consists of two layers of flexible vinyl film. Vinyl is vaportight and has a smooth surface. Soap and water can be used to clean it. Do not use ammonia detergents for cleaning because this bleaches the vinyl. WEBBINGS AND TAPES You already know that cloth is fabric wider than 12 inches. Any fabric less than 12 inches, from selvage to selvage edge, is called webbing or tape. The dividing line between webbing and tape is determined by the respective weight. Webbings The heavier of the two is webbing. Webbing weighs over 15 ounces per square yard and is less than 12 inches wide. As you would expect, webbings are used for the toughest holding and reinforcing jobs. Slings, harnesses, safety belts, reinforcing and securing straps are made of nylon, with a wide variety of tensile strength. The personnel parachute harness has a tensile strength range of 6,000 to 8,700 pounds. Some nylon webbings are of tubular construction, which makes them very strong. Tubular webbings are 1/2 to 1 inch wide, with tensile strengths ranging from 1,000 to 4,000 pounds. Tapes In addition to webbings, there are the lightweight tapes of a twill weave construction. You can use tapes for reinforcement on many types of fabric covers. Tapes can weigh up to 15 ounces per square yard. Cloth tapes are woven in the same manner as fabric. Some are bias, which, because of the bias cut or construction, aid the binding of curved edges where stretching qualities are desired. These bias tapes are sometimes referred to as binding tapes. Velcro tape is commonly used in many shops as a fastening or closing device. Velcro tape consists of two parts-the hook and the pile or loop tape. The hook tape is made of nylon, which consists of a series of small hooks. The nylon pile or loop tape has many small loops. When the two parts of the tape are joined, the hooks engage with the loops holding the two tapes together. DIFFERENCE BETWEEN THREADS AND CORDS The difference between threads and cords is discussed in the following text. Threads Filaments (nylon) or staples (cotton) are twisted together to form yarns, and two or more yarns are twisted together to forma thread or ply yarns, as the yarn by itself is too small for practical use. The strength of a thread depends upon the size and number of yarns used to make up the thread. The thread numbers on spools indicate the size of the yarn and the number of yarns that are piled (or twisted) together to give the necessary strength to the thread. For example, a 16-4 thread indicates that the thread was made from a single yarn, size 16, and that four of these single yarns were twisted together to make a thread. The finer the yarn used, the higher its size number. Silk and nylon thread sizes, however, are indicated by letters, such as A, B, etc.; A is finer than B; the farther down the alphabet, the coarser the thread. Thread is twisted to the left or twisted to the right, depending on its use. Left-twist thread is always used in the sewing machine because the action of the stitch-forming mechanism tends to ravel or break right-twist thread. Left- or right- twist thread may be used for hand sewing. The terms that designate left-twist threads are machine, machine twist, left twist, and Z twist. A cord or thread has left (or Z) twist if, when held in a vertical position, the twist of the yarn follows the slope of the central portion of the letter Z; and right (or S) twist, if it follows the slope of 10-4