DIN Standard 912. ISO Metric Threads A4 Stainless Steel, M6 - M12. This RS A4 Cap Head Socket Screw Kit contains 431 A4 stainless steel cap head screws in a range of metric thread sizes from M6 through to M12 size. These Socket Head Cap screws offer a greater tensile strength than equivalent Hex Head Cap screws whilst requiring less surface area to counter-bore. Applications:. Precision work Architectural metal-work Aesthetic improvements