WTF Magnaflow?

So I installed the magnaflow cat back I ordered (completed install sunday night, well almost). Everything went fine until tightening the bad clamp that connects the tailpipe to the exhaust. The directs state the band clamps must be VERY tight (approx 65 ft-lbs), so what do I do, get the the torque wrench and set it to 65 ft-lbs. While tightening down on the pass. side the bolt breaks, WTF? Needless to say I didn't torque the driver side. Guess I'll get a new clamp and put that on.
 
i sheared one of the U-Bolts connecting the muffler to the tailpipe. Couldn't find any stainless in town the same size.
Had to order a new one 11 bucks should be here tomorrow.
 
How do those band clamps work on two pipes of slightly different diameter? I bought some aftermarket exhaust pipe to go with my Magnaflow DI/DO muffler, but they seem to be of slightly different diameters...and I can't exactly slip one over the other either?

Do they seal well?