I’m running into a few issues trying to install my cat-back exhaust, which I thought would be an easy job. Like always it never goes as planned for me and I cannot fit my bolts into the y pipe-catalytic converter flange without hitting the cat itself. I couldn’t reuse the original studs on the car due to the rusted nuts, therefore I had to cut them. Now I’m either confused whether my flange is too banged up and bent or it’s just a bolt sizing issue. The other side of the flange seems to fit just fine.

 

You can see inside the hole there are those little grooves cut into it, those are for press-fit bolts.

What you probably need to do is buy some allthread that's the correct thread pitch to screw into your other side of the flange, then cut it down to length to make little "studs" that will poke through your catalytic converters in the picture. Then you use a nut on the back side.

If the y-pipe isn't threaded (I don't think it is, can't remember) then you can just use a nut on both sides.

Or run your bolt in backwards, put the bolt head on the y-pipe side and the nut on the catalytic converter side.

 

I ran into the same issue when replacing my Y-pipe, and just reversed the nut and bolt on on that side as Cleric mentioned. You may still need a shorter bolt than that though. I can't remember what length I used but it looks shorter than yours. It also gave me room to fit a box wrench on the nut.

 

Yes I did exactly that, originally if I flipped the bolt to the other side, the end of the bolt would hit the catalytic converters. So I went to the hardware store and bought m10x30 bolts, could be 35, don’t exactly remember. Luckily had enough threads left for the nut.