SHOULDER SLEEVE INSIGNIA: Description: On a yellow shield with a 1/8 inch (.32cm) blue border 2 9/16 inches (6.51cm) and 2 inches (5.08cm) in width overall, a blue millrind throughout.
Symbolism: The millrind is the iron reinforcement fixed in the center of a millstone to support the stone as it revolves on its axle when grinding wheat. It is used in heraldry as a symbol of support. With the additional reference to wheat, the "staff of life", the millrind stands for the vital and varied support furnished by the organization.
Background: The shoulder sleeve insignia was originally approved on 11 Feb 1966 for the 1st Support Brigade. On 15 Oct 1976 it was redesignated for the 21st Support Command. (http://www.21tsc.army.mil/21tsc/heraldry.asp)