exhaust clamp

I had a toyo manifold fitted and it was ok at the start. But now seems to be blowing alot, ive looked under and the clamp is bent. What size do i need for another so i can fit on?
Thanks all.
 
Thanks for that. Yes thats the one but i dont know if my exhaust is even straight as they had to put a flat on the manifold as was too close to subframe so im thinking that its some how forced it too high for the rest of the exhaust to be level.