('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'.
(..) - Get in the car! - Take them! Take them! #Adelante! Get in! #Olivia! Place yourselves belts. Where are we going? #We'll stay in Carol a while. Do not look back! #Everything will be fine. Lee and Mason. Take (..)2014 Boyhood
(..) - I'm going! - I want to go! Mason on the outward journey and Samantha in the back. #Top. - Seat belts! - Belts. Sure! #Do not forget the belts. Neither has this car seat. All right. All right. All right! Very well! (..)2014 Boyhood
(..) Family's running. The drive out was pretty fun. What was your favorite part? Spitting out of the car window. - Definitely not when Dad was singing. - Wearing the sit belt. Oh. What about the time with the dinosaur. - Oh, that's the one. - That was great. Say cheese. (..)2015 Inside Out