It seems like you're asking about NIJ (National Institute of Justice) IIIA armor, which is a standard for ballistic body armor in the United States. NIJ IIIA refers to a specific level of protection provided by the armor https://armored1.com/. NIJ IIIA armor is designed to stop handgun rounds up to .44 Magnum, including 9mm, .357 SIG, and .44 Magnum