Arrow Shaft Length and Labeling
Arrow shaft length also must be matched to your bow. Drawing an arrow that's too short is dangerous because it may slip off the bow, while an arrow that's too long adds unnecessary weight and weakens the spine of the arrow. Arrow tables can help you make the right selection.
Aluminum arrows are labeled by their outside diameter and the wall thickness of the shaft. For example, if an arrow is labeled 2013, the arrow has a 20/64-inch outside diameter and a 13/1000-inch-thick shaft wall. A thicker shaft provides greater stiffness.
Aluminum and carbon-fiber combination arrows are measured by spine deflection. The smaller the number, the stiffer the spine. For example, 3-60/340 means three wraps of carbon-fiber, with an aluminum core tube diameter of 60, and a spine stiffness rating of 340.
Carbon arrows also are labeled to indicate their spine deflection. The most common spine sizing values are 340, 400, and 500. As with combination arrows, a smaller number means the arrow has a stiffer spine. Therefore, a value of 340 indicates a stiffer and heavier spine while a value of 500 indicates the lightest and most flexible spine.