Sno-Stuff's Cylinder Sleeves are centrifugally spun from the finest cast iron material available. They are a combination carbon chrome alloy and Molybdenum. This material provides for easy installation, excellent boring, and honing characteristics, plus extra long life. (Note: This is the same material used most Heavy Duty Diesel engines.) Each sleeve undergoes strict quality and workmanship inspections to ensure they meet the highest quality standards.