Flat Washer Flat Washer Type Standard Dimensional Standards DIN 9021 Material Steel Material Grade/Class Grade 2 Finish Zinc Plated For Screw Size M18 Inside Diameter 20 mm Outside Diameter 56 mm Maximum Thickness 4 mm System of Measurement Metric Minimum Thickness 4 mm Maximum Temperature 302 Degrees F Minimum Temperature -58 Degrees F Pack Size Small Pack Package Quantity 25