Wireways and cable troughs are designed to protect electrical wires from dust, dirt, water and oil. There are three basic types of products: lay-in wireways, pull-through wireways, and cable troughs. Lay-in wireways are open on one side to allow the placement of wire without feeding through. Products are available in straight lengths of 6, 12, 18, 24, 30, 36, 48, 60, 72, and 120 inches (in). Pull-through (feed-through, sectional) wireways are also available. Nominal cross-sectional sizes include 2 in. x 2 in., 2.5 in. x 2.5 in., 3 in. x 3 in., 4 in. x 4 in., 6 in. x 6 in., 8 in. x 8 in., 10 in. x 10 in., 12 in. x 6 in., and 12 in. x 12 in. Other cross-sectional sizes are also available. Wiring troughs or cable troughs are completely enclosed and are often rated by the National Electrical Manufacturers Association (NEMA), a non-profit organization that recommends safety standards for electrical equipment. There are three basic cover styles for wireways and cable troughs: screw-on, snap-on, and hinged. Common materials of construction include steel, stainless steel, fiberglass, plastic and polyvinyl chloride (PVC).