Simpson Strong-Tie DCU Composite Screws. Engineered to provide beautiful fastening results for all types of composite decking while also offering greater ease of installation, a clean finish and superb corrosion resistance. The go-to-screw for all your composite decking applications, eliminating the need to mix and match screws to the decking. Available in carbon steel, as well as Type 305 and Type 316 stainless steel for high to severe levels of corrosion resistance, applications include fastening composite decking boards, etc.