original clamps and bolts and those made to original specs should be tightened until the short, top bend tab contacts the bottom, and then cottered. The pipe will slide within the clamp with some resistance, but not rattle. Many repro clamps and bolts are too small. Some clamps are for the Midas and other repro mufflers with the smaller tailpipe and are too small for a muffler made to Ford design. Many bolts have the cotter bores too far up the bolt so the bolt is tightened too tight. It all depends on what you are using. The tail pipe should not be clamped so tight it cannot move at all, nor so loose it rattles.