Sealed roller chains are a maintenance free, lube free roller chain commonly known as O or X ring chain because lubricant is contained by tiny O rings positioned between each inner and outer link plate. Lubrication is kept in due to the seal between the plates and most importantly dirt can be kept away from the bearing surfaces of the chain. This type of lube free chain provides better wear life than standard types of roller chain including traditional self lube roller chain. Some larger chains are fitted with an X rather than an O ring, reducing the friction coefficient on start up. Both O and X ring chains are used extensively on motorbike final chain drive.