('chiefly US') cities in the 'Rust Belt' [=an area formerly known for industry and manufacturing]
When you're riding in a car, you should always 'belt up' [=('US') 'buckle up'] for safety.
That remark was 'below the belt'. = That remark really 'hit' (him) 'below the belt'.
(..) -He don't even have a hat. -l do too have... My hat! -Told ya. -l found a spaceship! Showtime. Quick, get in. Fasten your seat belts. Close your tray tables. Hold on. lt might get a little bumpy. Three, two, one, blastoff! You saved us, cowboy. You're our hero. (..)2010 Toy Story 3