Installing 4" exhaust
 

I purchased an MBRP cat back exhaust system and am having problems installing it. The problem is with the adapter pipe that goes between the cat and the exhaust. It appears as though the adapter has a 4" inner diameter on one end which is correct. However the end that goes under the cat clamp is 3 5/8 outer diameter when it should be 3 1/2" outer diameter. Has anyone had similar problems or am I doing something incorrectly? Any help would be greatly appreciated.