Hexagon Socket ISO Metric Thread Class 10.9 – High Tensile Strength, Medium Carbon Alloy steel, quenched and tempered Countersunk head used with a countersunk hole providing a flush fit ‘As produced’ oiled finish (black) – Provides some shelf life but no real corrosion protection in use Min. Proof Load 830 Mpa DIN 7991 / ISO 10642 / BS 4168-8 / NEN 2359