Bicycle wheel some other fixed point may be used as a reference mark, however this is less accurate. At one end of each spoke is a specialized nut, called a nipple, which is used to connect the spoke to the rim and adjust the tension in the spoke. The nipple is usually located at the rim end of the spoke but on some wheels is at the hub end to move its weight closer to the axis of the wheel, reducing the moment of inertia. Until recently there were only two types of nipples: brass and aluminum (often referred to as "alloy").
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