Cortex Concealed Fastening System for Azek Trim is a fast and easy way to conceal fasteners and screw heads when installing PVC trim Boards. Cortex is easy-to-use and includes everything needed, including screws, plugs and setting tools. FastenMaster recommends installing with an 18 volt cordless impact drill. The Cortex for Trim Fastening System is designed for use with PVC Trim with actual thickness of 5/8" to 5/4". How many fasteners are needed? Horizontal trim boards less than 12" wide, use two Cortex fasteners at every framing member-rafter tail or wall stud. The screws should be 16" OC or closer. Vertical trim boards (i.e., next to a door or a window), use two Cortex fasteners every 16" OC or closer. If a trim board is 12" or wider, use three screws. Each trim board must be fastened within two inches of the end of each board. Note: Predrilling is not required throughout the majority of the project. Predrilling is required when fastening within 1/2" of the end of a board and at mitered joints. Use a 3/16" drill bit for predrilled pilot holes.