Iron Crates serve very little purpose and are indestructible except in Crash of the Titans where they contain mojo. They can serve as bridges for Crash Bandicoot to cross. They are often originally outline crates until Crash presses a ! crate, turning them into iron crates. They can also be dangerous if bouncing on top of iron arrow crates (crush hazard). Slot crates will also turn into them if they are not broken in time.