German sixth chord
A German sixth chord is a tetrad comprising a root, major third, perfect fifth, and augmented sixth, often built on the sixth degree of the minor scale.
In just intonation
Because the German sixth chord is often built on the sixth degree of a minor scale, the 128:160:192:225 found on the ♭VI of the duodene is a good candidate for its interpretation in the 5-limit.
In meantone
In meantone, the augmented sixth represents both 125/72 and 225/128. In the historically-prevalent quarter-comma meantone it is tuned only a few cents shy of a just 7/4, and in the closely related septimal meantone it explicitly represents 7/4 as well, so the meantone German sixth chord can be considered to approximate both 4:5:6:7 and 128:160:192:225.