Material/ Facts: Stainless steel in A4 (acid-proof) quality, Torx25 Function: Intended for mounting pressure-treated timber, e.g., in saltwater, pools, and hot tubs. The screw is more similar to a traditional wood screw than a decking screw. This screw is also suitable for use with Larch decking, as the acid in larch is aggressive, thus the larch decking must be pre-drilled.