This wood screw is excellent for use in many bolt building and industry where corrosion resistence is a requiement.Full body,cutting thread is for better fastenings in wood compared to rolled thread screw. It has 2/3 thread on shank.used mainly in marine and other projects. C65100& C65500 silicon bronze is an alloy of copper plus Si,Mn,Zn,etc.which is resistant to seawater corrosion and in planking of Boat.