NATIONAL manufactured the DUOLIAN between 1931 and 1940. The Duolian was a metal bodied single cone resonator guitar. The body was made of steel with two f-holes (flat cut until 1933 and then with rolled edges from 1933-1940). The necks were mahogany or maple with an unbound dyed (ebonized) maple fretboard and pearl or ivoriod dots. Early models had 19 frets and joined the body at the 12th fret. From 1934 onwards they had 20 fret necks which joined the body at the 14th fret. The headstocks were slotted with classical style tuners (3 on a plate).

NATIONAL made the STYLE N between 1930 and 1934

NATIONAL manufactured the single cone STYLE O resonator between 1930 and 1941. From 1933 this model featured rolled f-holes. In 1934 the number of frets to the body incresed from 12 to 14.

The first National Triolians were an introduced in 1928 as a cheap tricone model but only around 28 of these three cone models were made before National switched the design to a single cone. The original National Triolians had a wood body with twp flat cut f-holes and 12 frets to the body (19 frets in total) fingerboard. They had a green finish which was usually oversprayed with another color on the body neck, fingerboard, and peghead. The bodies also had decals (a bouquet design or for later models a hula girl design). In 1929 steel bodies replaced wooden bodies.