In 1991, the Air Force changed its NCO insignia so that a maximum of five stripes, or rockers, were placed on the bottom of the chevrons. The master sergeant rank insignia was changed by removing the bottom (sixth) rocker, and relocating it above as a single chevron, on top of the five lower stripes. The single chevron above visually identifies Senior NCO status for E-7 master sergeants along with two chevrons above for E-8 senior master sergeants and three chevrons above for E-9 chief master sergeants in the Air Force NCO insignia. In 2015, the Air Force announced its promotion overhaul and newly established boards for master sergeant.