D Major 6th
6
0 - 4 - 7 - 9Major + major 6th
About D Major 6th
D6 adds a B to a D major triad, and on guitar that means the open B string is already doing the work. Play a D shape without fretting the B string at all and the chord is there — which is why so many folk and country players use it without ever having decided to.
The notes
D, F♯, A, B. The B is the sixth, and it is one of the guitar’s open strings, so this chord costs less effort than the plain triad in some voicings.
The same four notes read from B give B minor seventh. In the key of D that equivalence lets a progression move between the tonic and the relative minor without changing shape.
Voicings
The open shape keeps the standard D fingering and lets the B string ring. A fuller version adds the low D on the fifth fret of the A string for weight.
Higher up, the D6 grip on the middle strings at the seventh fret is what swing rhythm uses — compact, no open strings, easy to mute between beats.
Adding the low D on the fifth fret of the A string is worth the reach in fingerstyle: without it the chord sits entirely above the open D, and the bass line has nothing to land on when the thumb comes down.
Where it shows up
As a tonic colour in D major, especially in fingerstyle where the open B rings against the melody. Country endings use it as a matter of course.
It also appears in Celtic and folk playing, where D is the default key and open strings are left sounding deliberately — the sixth arrives as a by-product of the tuning and stays because it works.