PTA Ruspro Series screws are coated with at least 25µ of Mech. Galv. Zinc – Tin with 20 – 30% Tin and Balance Zinc. Over and above mechanical plating, 2 top coats are given to further enhance corrosion resistance. PTA Ruspro screws strictly comply to following Class 3 requirements with various mechanical and dimensional properties and treated appropriately to obtain the optimal performance. Therefore, using a PTA screw that has been produced to meet the Australian Standards AS3566 ensures you that the screws can be safely used externally in mild, moderate industrial or marine applications. The corrosive categories of the environment where these screws can be used are C2 and C3 classified in accordance with ISO 9223.