Bicycle wheel metal or carbon fiber rim which holds a pneumatic rubber tire. A hub is the center part of a bicycle wheel. It consists of an axle, bearings and a hub shell. The hub shell typically has two machined metal flanges to which spokes can be attached. Hub shells can be one-piece with press-in cartridge or free bearings or, in the case of older designs, the flanges may be affixed to a separate hub shell. The axle is attached to dropouts on the fork or the frame. The axle can attach using a: Modern bicycles have adopted standard axle spacing: the
Ship's wheel (though sometimes as few as six or as many as ten) shaped like balusters and all joined at a central wooden hub or "nave" (sometimes covered with a brass "nave plate") which housed the axle. The square hole at the centre of the hub through which the axle ran is called the "drive square" and was often lined with a brass plate (and therefore called a "brass boss", though this term was used more often to refer to a brass hub and nave plate) which was frequently etched with the name of the wheel's manufacturer. The outer rim is composed