A typical inline skate wheel consists of one rubber wheel (usually with an aluminum core), two bearings, and a spacer. The spacer holds the bearings apart so that the outer edge of each bearing lines up with the outer wheel edge, and the axle goes through the spacer to hold the wheel assembly in the frame. In recreational and fitness skates, the frame is generally part of the boot. In speed skates, the skate frame is replacable with tools. Hypnos are a variant of recreational skates.