The Stainless 303 Grade Holder is specifically designed to be used with 42.4mm newel posts. It serves as a holder for going through the middle of the newel post, providing additional support and stability. Made from high-quality 303 grade stainless steel, it offers excellent durability and corrosion resistance. Please note that a 5mm screw is required to attach the holder to the side of the newel post, and it is sold separately.