For me, it's a 2000 Gibson Blackbird that has been modded with a V/V/T/T set up and three way toggle as opposed to the standard on/off switch. The pickups sound completely different than any other T-bird I've ever played, and have more output and cleaner and deeper lows. Unlike the regular Thunderbird IV's - the Blackbird features a slightly thinner nut (on mine at least), has an ebony fretboard, and has a three piece all mahogany neck as opposed to the multiple walnut/mahogany laminations on the IV. I recently set my IV up with a V/V/T/T and three way, and hope to someday come across a set of Blackbird pups to drop in it so I can switch between the two basses during a show without having to make drastic level and EQ changes. I really don't care that the Blackbird is technically a "Nikki Sixx Signature" bass- for me I dig it because of the way it plays and sounds.