Based on the succesful ZDP189 line, master Hanaki adapted the next generation powdered stainless steel from Hitachi Special Steel. Compared the ZDP189, the HAP40 has less carbon content but offers even higher rockwell hardness hence offering even better edge retention. The HAP40 also offer better toughness compared to the ZDP189. This is the choice for those looking for the absoute best steel for edge retention. Sukenari has a very long history making single bevel knives for famous knife brands like Masamoto and Aritsugu, as a result their single bevel blades are highly appreciated by professionals in Japan.