"0" is used to identify personnel undergoing training for award of a primary MOS (PMOS).
"1" identifies a private (PVT) through specialist (SPC/pay grade E-4) or corporal (CPL/also pay grade E-4)
"2" identifies a sergeant (SGT/pay grade E-5)
"3" identifies a staff sergeant (SSG/pay grade E-6)
"4" identifies a sergeant first class (SFC/pay grade E-7)
"5" identifies a master sergeant (MSG) or first sergeant (1SG) (see E-8, below)
"6" identifies a sergeant major (SGM/pay grade E-9) or command sergeant major (CSM/pay grade E-9) (as of 1 April 2011)
https://en.wikipedia.org/wiki/United_States_military_occupation_code#Current_Day