Zinc Plated Cast Iron Bolt Nut and Washer This set contains an M6 x 25mm bolt, a nut and a washer, manufactured from cast iron, but with a zinc plating through galvanisation. The zinc coating provides a surface that is resistant to corrison, and acts as a sacrificial coating that wears down over time, but protects the cast iron surface from being exposed. An M6 bolt is a bolt that fits a 6mm hole. Unsure if this zinc plated cast iron bolt nut and washer is suitable for you? Call our team on 01752 692760 or use the live chat and they will help identify the correct bolt, nut and washer for your project.