Fuller

A fuller is a groove positioned into the surface of a blade in order to lighten the blade. The loss in strength of the blade is reduced as the centre of a blade does not significantly undergo either tension or compression during a cutting stroke.

During a thrust, however, the groove weakens the blade if the fuller is large. Consequently thrusting blades such as a rapier typically have a diamond blade cross-section.

This groove may be found at the back of a backsword or in the centre of a two-edged sword.