Ball bearings, in the context of yo-yo play, were introduced in the early 1990s. They are used to reduce friction while the yo-yo is sleeping. A ball bearing yo-yo can be played in two extreme states. One configuration involves using a thick lubricant in the ball bearing, so that sleep times will be low. This configuration is generally used for looping tricks. The second configuration involves either running a bearing with thin lube in small amounts or cleaning the ball bearing of any lubricant - playing a "dry" bearing. Dry bearings are usually used so yo-yos will be less responsive during string trick play.