A fuller is a rounded or beveled groove or slot in the flat side of a blade (e.g. a sword

Sword

A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...

, knife

Knife

A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

, or bayonet

Bayonet

A bayonet is a knife, dagger, sword, or spike-shaped weapon designed to fit in, on, over or underneath the muzzle of a rifle, musket or similar weapon, effectively turning the gun into a spear...

). A fuller is often used to lighten the blade

Blade

A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...

, much in the way that an I-beam

I-beam

-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...

 shape allows a given amount of strength to be achieved with less material. Longer knives or bayonets intended as offensive weapons may employ fullers (also incorrectly known as 'blood grooves') to lighten the blade while maintaining its strength. 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 without any sacrifice of strength or blade integrity. This effect lessens as the blade is reduced in length. Short bladed knives may employ fullers simply for their aesthetic effect.

Physics

The basic design principle is that bending

Bending

In engineering mechanics, bending characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically...

 causes more stress

Stress (physics)

In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...

 in material near the edge or back of the blade than material in the middle, due to lever

Lever

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

age. The diagram at right shows stress distribution in an ideal blade with a rectangular section, with only a small amount of shear stress present at the neutral axis. Fullers remove material from near this neutral axis, which is closer to the blade's spine if only one edge is sharpened (see photo above). This yields stiffer blades of a given weight, or lighter blades of a given stiffness

Stiffness

Stiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom when a set of loading points and boundary conditions are prescribed on the elastic body.-Calculations:...

. The same principle is taken to an extreme in the H-shaped cross sections of most steel beam

Beam (structure)

A beam is a horizontal structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.- Overview...

s. Some contend that this concept was borrowed into architecture from weapons design.

Japanese blades

In Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

ese bladesmithing, fullers have a rich tradition and terminology, enough that there are separate terminologies for the top (hi, usually pronounced as bi when used as a successive word) and bottom (tome) ends of the feature. A listing follows:

• Hi
  • Bo-bi: A continuous straight groove of notable width, known as katana
    Katana
    A Japanese sword, or , is one of the traditional bladed weapons of Japan. There are several types of Japanese swords, according to size, field of application and method of manufacture.-Description:...
    
    -bi on tantō
    Tanto
    A is one of the traditional Japanese swords that were worn by the samurai class of feudal Japan. The tantō dates to the Heian period, when it was mainly used as a weapon but evolved in design over the years to become more ornate...
    
    . With soe-bi, a secondary narrow groove follows the inner straight length of the main one. With tsure-bi, the secondary is similar but continues beyond the straight length.
  • Futasuji-bi: Two parallel grooves.
  • Shobu-bi: A groove shaped like the leaf
    Leaf
    A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
    
     of an iris plant
    Iris (plant)
    Iris is a genus of 260-300species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, referring to the wide variety of flower colors found among the many species...
    
    .
  • Naginata-bi: A miniature bo-bi whose top is oriented opposite from the blade's, and usually accompanied by a soe-bi. Seen primarily on naginata
    Naginata
    The naginata is one of several varieties of traditionally made Japanese blades in the form of a pole weapon. Naginata were originally used by the samurai class in feudal Japan, and naginata were also used by ashigaru and sōhei .-Description:A naginata consists of a wooden shaft with a curved...
    
    s.
  • Kuichigai-bi: Two thin grooves that run the top half of the blade; the bottom half is denoted by the outer groove stopping halfway while the inner one expands to fill the width.
  • Koshi-bi: A short rounded-top groove found near the bottom of a blade, near to the tang.
• Tome
  • Kaki-toshi: The groove runs all the way down to the end of the tang.
  • Kaki-nagashi: The groove tapers to a pointed end halfway down the tang.
  • Kaku-dome: The groove stops as a square end within 3 cm of the tang's upper end.
  • Maru-dome: Similar to the kaku, except with a rounded-end.

The kukri

The Nepal

Nepal

Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

i kukri

Kukri

The kukri is a curved Nepalese Knife, similar to the machete, used as both a tool and as a weapon...

 has a terminology of its own, including the "aunlo bal" (finger of strength/force/energy), a relatively deep and narrow fuller near the spine of the blade, which runs (at most) between the handle and the corner of the blade, and the "chirra", which may refer either to shallow fullers in the belly of the blade or a hollow grind

Grind

The grind of a blade refers to the shape of the cross-section of the blade. It is distinct from the type of blade , though different tools and blades may have lent their name to a particular grind.Grinding involves removing significant portions of metal from the blade and is thus distinct from...

of the edge, and of which two or three may be used on each side of the blade.