The two cats were about 1.5 inches closer together. Probably the front end bent in transit. I pulled them apart by hand until I could get the screws to start multiple threads. Then I turned each screw the same way until they had the flanges flush back in place. Difficulty: Pretty hard for a shady tree like me. A pro will consider it another day at the office. The result: no leaks, no codes. She runs like a champion with noticeably more panache.