What's the difference between a powerlifting bar and an Olympic weightlifting bar?

Powerlifting bars are stiffer (less whip), use a 28.5–29 mm shaft, often have center knurling, and typically run on bronze bushings for slow, controlled spin under heavy squats, deadlifts, and bench. Olympic weightlifting bars use needle bearings for fast sleeve spin (essential for cleans and snatches), have a thinner 28 mm shaft with more whip, and usually omit center knurling. Most barbells in this pool are marketed as 'multi-purpose' bars that compromise between the two.