A fuller is a rounded or beveled longitudinal groove or slot along the flat side of a blade (e.g., a sword, knife, or bayonet) that serves to both lighten and stiffen the blade. It is made using a blacksmithing tool called a fuller, a form of a spring swage, or impressed during forging. When combined with proper distal tapers, heat treatment and blade tempering, a fullered blade can be 20% to 35% lighter than a non-fullered blade, yet also stiffer, thanks to having two reinforcing ridges created by the opposing sides of the fuller. This stiffening effect increases dramatically with blade length. A fuller is often used to widen a blade during smithing or forging. Fullers are sometimes inaccurately called blood grooves or blood gutters. Channelling blood is not the purpose of a fuller. Etymology The term "fuller" is from the Old English fuliere, meaning 'one that fulls [pleats] cloth'. It is derived from the Latin word fullo. The first recorded use of the term in relation to metal working is 1587. The first recorded use of the term to describe a groove or channel in a blade is 1967. Tool As a blacksmithing tool, a fuller is a type of swage, a tool with a cylindrical or beveled face used to imprint grooves into metal. Fullers are typically three to six inches long. If a groove is to be applied to both sides of the steel, two fullers may be used at the same time, sandwiching the workpiece in the middle. Often, one fuller will have a peg that holds it securely in the anvil, while the other fuller will have a handle and a flat head, for striking with a hammer. A blade being fullered will generally be slowly pulled through the fullers as it is being hammered, displacing material to the side (rather than removing it) and thereby creating ridges on either side of a groove. These ridges may be hammered flat, widening the blade, or they are often shaped with other swages, increasing the strength of the blade both by creating thicker areas in its cross section and lateral ridges that resist lengthwise deflection. In addition to being used to "draw out" steel, hammering a short block into a long bar, fullers are also used in the production of items such as hinges and latches, plow parts, and horseshoes. Japanese blades In Japanese swordsmithing, fullers have