Set the screw. Set the plug. You are all set! Cortex Concealed Fastening System for Trex Decking is the perfect way to conceal the fasteners on your new Trex deck. Cortex utilizes traditional face fastening methods so there is no need to learn a new clip system or work at odd angles under the deck. Cortex plugs are made out of the same Trex material which eliminates issues with expansion, contraction or wear. Plus, Cortex fastens all parts of your decking project first board, last board and stairs and is less expensive than virtually any other hidden fastening system on the market. 100 and 300 sq ft kits come complete with everything you need to complete your job: screws, plugs and bits.