Fuller (groove)

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, when considering its reduced weight.^[1]

Cutting or grinding a fuller into an existing blade will decrease its absolute stiffness due to the removal of material, but much of the strength remains due to the geometry of its shape. When the groove is forged into the blade, it achieves a similar reduction in weight with a relatively small reduction in strength without the wasted material produced by grinding.^{[citation needed]} When impressed during forging, it may be made using a blacksmithing tool that is also called a fuller, a form of spring swage.

When combined with optimal^[vague] distal tapers,^[2] heat treatment and blade tempering, a fullered blade can be 20% to 35% lighter than a non-fullered blade. The ridges and groove created by the fuller are comparable to an I-beam's flanges and web; this shape aims to optimize the strength and stiffness for a given quantity of material, particularly in the cutting direction.^{[citation needed]}

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.^[3][4][5]