>Stringers
In aircraft and launch vehicle construction, a longeron, or stringer or stiffener, is a thin strip of material to which the skin of an aircraft or propellant tank may be fastened.
The longeron system also requires that the fuselage frames be closely spaced (about every 4 to 6 in or 10 to 15 cm). If the longitudinal members are numerous (usually 50 to 100) and are placed just between two formers/frames, then they are called "stringers". In the stringer system the longitudinal members are smaller and the frames are spaced farther apart (about 15 to 20 in or 38 to 51 cm)
~ en.wikipedia.org/wiki/Longeron