https://www.sargeknives.com/faq"We use 440A and 440C. 440 A – 440 B – 440C The carbon content (and harden-ability) of this stainless steel goes up in order from A (.75%) to B (.9%) to C (1.2%). 440C Stainless Steel is an excellent, high-end stainless steel, usually hardened to around 56-58 Rc compared to 440A around 52-54Rc. All three resist rust well, with 440A being the most rust resistant, and 440C the least. Many high end dive knives are made using 440A. 440C is consider by many as the ultimate general-use stainless. If your knife is marked with just “440", it is 440A; because the 440C is a more expensive, we want to advertise that. Our feeling is that 440A is well suited for everyday use and 440-C is excellent."