The Halo series of bearings are a high quality steel/chrome bearing with metal shields. These bearings have been tested and proven by many racers.
The 3x8x4 Metal 633ZZ bearing is commonly used in the T-Rex 450 X, XL, SE Helicopters and in the Thunder Tiger Raptor 30 helicopter (seesaw bearings and uses 6 of them). Check your manual for the correct size for your vehicle if you are not certain.