Sea-Dog 18/2 AWG Flat Duplex Wire Red/Black - 500' [8018207]18 2 AWG Flat Duplex Wire Red Black 500' Tinned Copper Stranded Wire. Sea Dog Marine Wire is offered in 16 2 6 2 gauges for duplex boat cable installations. All duplex cable is sheathed in PVC and is flat in construction. It is designed and manufactured for marine use with tinned copper wire for corrosion resistance and improved conductivity. The copper is annealed and finely stranded to offer flexibility and resistance to vibration to ensure reliable