First thing to realize about this clamp, is that their are currently 8 rear tailpipe clamps being made. We do not know which one you have. If it has a square hole and a carriage bolt, then it is a cheap Chinese one. Throw it away. Buy a good one that uses a bolt with a castle nut and cotter pin, as you do NOT want it tight. The tailpipe /muffler assembly grows by roughly an inch when it gets warm, and must slide in that rear bracket or it will bend at the front and leak.
Steve Becker
Berts Model A Center