I looked in the exhaust stickies for the metric bolt sizes, but did not see them....please tell me what bolt size connects the flex of the y-pipe (budget) to the cat (oem). Also does it matter what size the rest of the bolts are that connect the cat back? Thanks in advance...

 

I think they're 14mm, and what do you mean does it matter what size the cat-back bolts are?

 

The stock cat should have studs and nuts, not bolts.

Either way, 12x1.25.

What do you mean by what size for the rest? Connect the catback to the cat, or connect the individual catback pieces to eachother? If to the cat, then 12x1.25 nuts, if the rest of the exhaust, and it has regular drilled flanges then it doesn't matter what size.