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").
Tire Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tire has reached its wear limit. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tires are fully worn and should be taken out of service. Most wear bars indicate a remaining tread depth of and are tires are deemed "worn out" when the tread is worn down to that point. The tire bead is the part of the tire that contacts the rim on the wheel. The bead is typically reinforced