The Halo ceramic series of bearings are a high quality steel/chrome bearing with metal shields and ceramic Si3N4 balls. This is the common bearing used in the Team Losi XXXNT clutches (these are non-flanged, standard for the Drake edition)
1/4 x 3/8 x 1/8 Halo bearing by Avid Racing Concepts is the standard bearing for nitro clutchs. Check your manual for the correct size for your vehicle if you are not certain.