A 1.75" vane, for example, may be enough for a 28" arrow but may be incapable of adequately stabilizing a 31" arrow. A longer vane may be advantageous for a long arrow. The longer the vane, the more stable it is, but the longer the vane, the more it will cost you in feet per second speed. A very long vane (3") or 4" would be appropriate for a fast bow. The amount of vanes you need depends on how long your arrow is and what type of stabilization you want to achieve. At least two small vanes are needed on each side of the arrow to provide adequate stability. Arrows with longer vanes tend to be more stable than those with shorter ones. However, longer vanes reduce the rate at which the arrow travels through the air. The type of vanes you need will depend on how much weight you want to carry and where you intend to shoot your arrow. Arrows with plastic vanes are less expensive than those with metal vanes but will not withstand wind as well. Metal vanes can be bent out of shape if hit by tree branches or other objects on its way to the target but will still provide some degree of stability even if damaged. Generally, people choose arrows that fall within a certain price range and use their judgment to select arrows that will do the job.