Originally Posted by
nkedel
...which in turn comes from the fuselage diameter of the 707 (designed mid-50s) itself widened from an early military design. The DC-8 set the current 6-across narrow-body pattern, even though (because it was already in progress) the 707 released first.
Yup. It goes way back. I still like flying on the 737's, even if they are just barely wide enough for what they do.