This Pypes brand cat kit has metallic substrate cats. These cats are heavy duty and designed for supercharged and turbo applications. They can also be used in a stock application if you think you may be getting a power adder in the future. They are a great way to tame down the exhaust note of your off road exhaust system. These cat kits are a direct splice in kit with no welding required. Simply cut a 2.5” diameter section out of your pipe and slide this in. Two cats and clamps are included. They also have threaded holes if you want to use 02 sensors. A plug is included if you are not using o2 sensors. Like most aftermarket cat kits these are not 50 state legal. You should check your local and state ordinance for your specific regulations.