M3 Cap Head Range DIN 912 ~ Socket Cap Head A2 Grade M4 Cap Head Range DIN 912 ~ Socket Cap Head A2 Grade Socket Cap Head Screws Socket cap head screws are all A2 grade stainless steel with the recognised standard - DIN 912. This grade of screw has excellent corrosion resistant properties with added strength over low grade self tapping screws found in most RC model kits where the screws fix in to resin components.