This is a six piece instrument, with a head-joint and centre joint, two tuning-slides and two foot-joints. Simply by switching the D tuning slide for the Eb slide, and the D foot-joint for the Eb foot, the player transforms the D Pratten into an E-flat Pratten.

The exceptional tuning in both Eb and D is made possible by design elements in the bore and acoustic engineering in the foot-joint. It is further assisted by skillful undercutting during the final tuning process.

Although the centre-joint and head-joint are retained for both iterations of the Combo, it is curious to note that the tone character of the Eb often sounds playful and quite different from the more serious character of the D.