M3 Cap Head 12.9 Brite Zinc Plated Range DIN 912 & BS4168 ~ Socket Cap Head 12.9 Grade Brite Zinc Plated (CR3) Socket Cap Head Screws 12.9 Grade (High Tensile with Brite Zinc Plating) Socket cap head screws are all 12.9 grade high tensile steel with the recognised standard - DIN 912. These are the highest strength grade of screw available in M3, typically used on the Schumacher CAT for the the front/rear inner hinge pin blocks, due to their tensile strength over lighter grades like stainless steel.