Corrosion-resistant, stainless steel tongue and groove board screws. Lost head allows the screw to be driven, without a pilot hole, into the tongue without splitting the board (excluding hardwood). Twin thread tip for a balanced and true start. Tri-Lock TS thread eliminates timber split and thread form prevents the board from lifting. Fixes flush as the screw seats beneath the tongue and is removable. Ideal for exterior cladding and boards. Supplied with TX10 driver bit.