Background Trimming (Oval) Description
On an ultramarine blue oval-shaped embroidered item, with a 1/8 inch (.32cm) white border, 1 3/8 inches (3.49cm) in height and 2 1/4 inches (5.72cm) in width overall, a white lozenge throughout. 

History
The background trimming was approved on 20 November 1951.  It was amended to include metric measurements on 20 February 1991. The trim was amended on 4 May 2001, to include a white border.

Source: The US Army Institute of Heraldry