120mm Black Coated Slate Hooks Point Driven - 316 Grade (Box of 500) The slate hook is an alternative to the copper nail and can be used for fixing roofing slates on the roof application. The length of hooks required equals head lap 2-3mm. Hooks are made of stainless steel of various grades (304/316) coated or not. Only stainless steel of minimum grade 304 or better, 316 can be guaranteed. Only the 316 grade can be guaranteed in industrial areas or severe coastal exposure (front of sea). The coating is purely decorative and does not influence the resistance to corrosion of the material. The coating will usually last ten years or more, except in very abrasive conditions (salted winds for instance). Hooks are often used when making small repairs or replacing individual slates on the roof.