M3 Hexagon Dome Nut - A4 Stainless Steel - See Diagram for dimension key: d = 3 mm Thread Pitch - 0.5 mm m = 2.4 mm h = 7 mm s = 5.5mm A4 grade stainless steel is also known as type 316 S31.This has a greater corrosion resistance than A2 in certain environments, and is often used for Marine applications especially when coming into direct contact with salt water DIN1587