The slotted hex washer head Crete-Flex stainless steel screw is a self-tapping masonry screw fastener that can be used in solid concrete, brick or block material. Crete-Flex SS4 fasteners deliver corrosion resistance, enhanced ductility, high pull-out and shear values, and installation consistency to ensure reliable performance. Crete-Flex SS4 fasteners are the result of Elcos unique engineering technology. Unlike case hardening (the typical heat treat given to 410 stainless fasteners), Crete-Flex fasteners receive a proprietary, dual-heat-treating process that maximizes corrosion resistance and ductility. Crete-Flex fasteners then receive Elcos unique Stalgard coating process The combination of this unique heat treatment and silver Stalgard finish results in superior corrosion resistance. Even after 2,400 hours in a salt spray cabinet (per ASTM B117), Crete-Flex fasteners show no signs of red rust.