The Revolution Series bearings are a low friction bearing with several options to help satisfy anyone's desire. What makes this bearing unique is that it has a rubber seal on one side while having a metal shield on the other. Rubber seals are great protectors against dirt but the price is that they offer a little more friction due to the tighter seal.
5x13x4 Revolution bearing by Avid Racing Concepts is a popular bearing for Losi 8ight, Serpent, and Agama clutches. Check your manual for the correct size for your vehicle if you are not certain.