Walker is your one-stop exhaust shop, offering a full line of mufflers, pipes, hardware and accessories. Cat to Y pipe intersection showing after cat O2 sensor location. This qualifies as one of the STRANGEST stock exhaust parts I have seen. For some reason Toyota/Lexus decided to weld a straight section of 60mm pipe to the cat outlet flange, angle cut it, weld a 50mm pipe pipe that has its last couple of inches expanded to 60mm and match angle cut. Also note the O2 placement is in the 50mm sections of the Y pipe where the sensor tip takes up a good portion of the available flow area.
Cat-back exhaust systems will include any pipes that run from the catalytic converter to the muffler, the muffler itself, any pipes that may run from the muffler to the exhaust tips, and the exhaust tips themselves. Some cat-back exhaust systems have a muffler delete, which means no muffler is included. This is typically found on vehicles that function primarily for off-road use