: Hardness levels vary by size to ensure durability without becoming brittle: Size ≤ 6 mm : Minimum 52 HRC. Size 7–8 mm : Minimum 50 HRC. Size 10–14 mm : Minimum 48 HRC. Size ≥ 17 mm : Minimum 45 HRC.
: Standard metric sizes typically range from 0.7 mm to 36 mm . din 911 pdf