Exhaust keeps blowing

So I've noticed my exhaust keeps blowing from the same spot. It seems to be coming from the join between the first and second catalytic converters. I recently fitted a Scorpion cat back system and definitely made sure it wasn't blowing before I finished. I don't know if I'm missing a hanger... There seems to be a lot of weight just being held on by the hanger just in front of the rear axle and the manifold. Especially with the join only being secured by one of those 'U clamps'. Any ideas?
 
Ahh ok. Don't suppose you happen to know what thread size it is? Can't seem to find the dimensions anywhere. Found the clamp with standard bolt on Renault Parts Direct