The appropriate spacing between cage bars for a cockatiel is crucial to ensure the bird's safety and prevent escape. The bars should be no more than 5/8 inch apart. This spacing prevents the cockatiel from sticking its head through the bars, which could potentially lead to injury. Additionally, it's important that the cage bars are made of sturdy, non-toxic material to withstand the bird's chewing. Proper bar spacing, combined with a safe and engaging environment within the cage, helps maintain the cockatiel’s physical and mental well-being.