Corona FE404004XS0CD Extra Slim Taper File Carded, 4-Inch Superior Hardness - Carbon combined with precise heat treatment increases strength, yield strength (elastic limit) and hardness Superior Resistance to Abrasion and Corrosion - Chromium added to increase the resistance to corrosion and abrasion Superior Cutting Performance - More effective tooth angle and precise forming of the teeth Consistent Quality - More than 100 controls are performed on raw materials, products in process and finished products Limited lifetime warranty