 A key difference between the two was that the Duo Jet was not a true solid-body, instead being semi-solid with routed channels and pockets inside.The name Duo Jet was inspired by the guitars two pickups (Duo) and the advanced aircraft of the day (Jet).It was the first Gretsch guitar to have the truss rod accessible through the headstock, a pickup selection switch and a master volume on the cutaway.