What size are the bolts that connect to the Cat and the front ones on the headers?

I have a 2k1 Cali spec.

 

Well the front bolts That connect to the lower part of the cali-spec manifold requires 3bolts. I got them at my local hardware store if you did not receive any. Try to get Zinc plated or something better so it can deter rust a bit better. I also used the same bolts for the rear part of the Ypipe that connected to the Cat (in my case to the straight pipe).

I think the bolts I got were 5/16" and I believe 1.5" long.

Dixit