Spoke nipple
Encyclopedia
Bicycle wheel
A bicycle wheel is a wheel, most commonly a wire wheel, designed for bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels....
's rim to each spoke
Spoke
A spoke is one of some number of rods radiating from the center of a wheel , connecting the hub with the round traction surface....
.
The spoke nipple is a headed cylinder with threading
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
on the inside through part of its length (there is an unthreaded lead-in nearest the "flats"). The nipples will fit in holes in the rim, so that the head of the nipple is on the outermost part of the rim, while the other end of the nipple points inwards towards the hub. The threading grasps the spoke, so turning it increases or decreases tension
Tension (mechanics)
In physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
in the spoke and influences the position of the hub relative to the rim.
Since spoke threading and nipple threading must match, boxes of spokes usually include a like number of nipples. Weight savings or the need for great strength due to building a wheel with few spokes might call for obtaining different nipples than those shipped with the spokes. Standard materials for nipples are brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
(usually nickel-plated) and aluminum. Brass is heavier but more durable and less prone to corrosion, rounding of flats while tightening, and breaking; aluminum is far lighter. If using aluminum nipples, the spokes should be long enough to engage the full length of spoke nipple threads so that the load is carried from spoke to the top of the nipple. If the spoke is only part way into the nipple, the nipple carries the tension load and is prone to breaking from fatigue failure. Also, with aluminum nipples care and a good spoke wrench are needed to avoid rounding the flats while tightening. Recently, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
nipples have become available in the US from Titan Wheel Technologies. The theory behind titanium nipples is that they combine the advantages of brass and aluminum nipples (strength and weight, respectively), while also being far more corrosion resistant.
If the underside of the nipple has the traditional conical shape, the nipple tends to adjust perpendicular to the nipple seat of the rim
Bicycle wheel
A bicycle wheel is a wheel, most commonly a wire wheel, designed for bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels....
when the spoke is tensioned. This can cause a marked bend in the spoke where it exits the nipple, especially on small wheels with large diameter hubs, and subsequent early spoke failures. Nipples with a spherical contact surface to the rim that do not exhibit this tendency have been introduced (Sapim Polyax, DT ProHead).