Boomtubes are either Chrome or Stainless extender pipes that stick out the back. It takes the pipe from a 3" exit to a 4". They also come in different lengths from about 12"-18". They don't really do anything for performance they just modify the reverb of the exhaust. Im not sure what brand I have on my setup I just had the shop that bent my pipes put them on for me, if I had to guess I think they were Gibson. Im sure most custom muffler shops will have a display with them (every shop I went to did).