The bajo sexto is a member of the guitar family, and physically looks like a cross between a 12-string guitar and a cello because of its size. However, there are important differences: The body is usually a bit deeper; the neck is shorter, joining the body at the 12th fret (modern 12-string guitars usually join at the 14th fret); and (being a bass instrument) the strings are thicker. Older instruments tended to have a larger body; modern instruments are more guitar-like, and the body is typically not more than an inch or so deeper than the guitar. Modern instruments frequently have a cutaway in the upper bout of the body adjacent to the neck, allowing easier access to higher playing positions on the neck, for the left hand.[4]

Since the instrument is tuned an octave below the guitar, the body on some instruments is not large enough for the lowest E to resonate well, and many players remove the sixth course, playing on only 10 strings (five courses). Luthiers eventually picked up on this practice and began leaving off the low E course during construction, producing instruments with only five courses — bajo quintos.[6][better source needed]

Bajo sextos are traditionally tuned in fourths, what a guitarist would call all fourths tuning. The lower three courses are doubled at the higher octave (similar to the lower four courses on a 12-string guitar), and the upper three courses are doubled at the unison:

E1-E2    A1-A2    D2-D3    G2-G2    C3-C3    F3-F3(from lowest to highest course)

The bajo quinto derives from the bajo sexto. Bajo quintos eliminate the low E course and are tuned as follows:

A2-A1    D3-D2    G2-G2    C3-C3    F3-F3(from lowest to highest course, notwithstanding the first two pairs listed here as "highest to lowest".)[6]