Former

A former is an object, such as a template, gauge or cutting die, which is used to form something such as a boat's hull.

A former may become an integral part of the finished structure, as in an aircraft fuselage, or it may be removable, being used in the construction process and then discarded or re-used.

The primary purpose of formers is to establish the shape of the fuselage and reduce the column length of stringers to prevent instability.

[1] Formers are typically attached to longerons, which support the skin of the aircraft.

The "former-and-longeron" technique (also called stations and stringers) was adopted from boat construction,[2] and was typical of light aircraft built until the advent of structural skins, such as fiberglass and other composite materials.