The Chicago Iron Octavian Plus is an Octave/Fuzz pedal in the same style that Jimi Hendrix used to use. The plus version has two footswitches to allow for turning the octave on and off, as well as the effect on and off. It also features a switch to go between a "60's" and a "70's" mode of the pedal.
Billy is seen using this pedal in the Premier Guitar "Rig Rundown" of his Oceania tour rig. In that video he says "This is the exact clone of Jimi Hendrix's Octavia, I use that for a few things"
[Rig Rundown Video]