A bolt or quarrel is a dart-like projectile used by crossbows. The name "quarrel" is derived from the French word carré, meaning square, referring to their typically square heads. Although their lengths vary, bolts are typically shorter and heavier than traditional arrows shot with longbows. Parts of the bolt Point The point, also called the head or the tip, is the pointed and weighted front end of the bolt, which is sharp and hard so that it can penetrate the target. Shaft The shaft is the main body of the bolt to which other parts of the bolt are attached. In modern times it is normally made of carbon fibre or aluminium alloy (or sometimes both aluminum and carbon fibre are used), and is very lightweight for its strength. Shafts come with varying degrees of stiffness — referred to as the "spine" of the bolt. The more resistant to bending a bolt is, the more "spine" it is said to have, and a crossbow with higher draw weight ideally needs to be paired with a heavier bolt point and higher spine specifications. The weight of a shaft is usually in grains, and product descriptions may provide the total weight in grains, or in grains per inch (GPI), for which the total weight of shaft can be calculated by multiplying the GPI value with length of shaft in inches. Fletching Fletchings, also referred to as vanes, are fins located at the rear end of the shaft just before the nock. The fletching is typically made from soft light materials such as feathers, plastic or silicone rubber. They stabilize the trajectory of the bolt via three different means: resisting pitching and yawing of the shaft by acting like a stabilizer fin (fin-stabilization); reducing deviation from the longitudinal axis by creating a back-pulling center of pressure behind the bolt's center of mass (drag-stabilization); and in some particular cases, creating a rotation around the longitudinal axis (spin-stabilization) by having the fletchings mounted at a slight angle of attack. There is no rule or formula for determining the length of fletching needed — generally the longer the shaft is, the longer the fletching needs to be, and vice versa. Nock A nock is a small notched piece that is attached to the rear end of the shaft, for engaging and receiving the propulsive push from the string during shooting. Nocks are made of either plastic