équerre

Équerre is a term used in French to denote a tool or concept related to right angles. In everyday use, it refers to a device that helps form or verify a 90-degree angle, essential in construction, carpentry, drafting, and metalworking. It can also denote the right angle itself, or the concept of a perpendicular relationship between lines.

The most common forms are the carpenter’s square and the set square used in technical drawing. The carpenter’s square is typically L-shaped, with two arms forming a 90-degree corner and often marked with rulers along the edges. The set square, a triangular ruler used in drafting, usually includes 90 and 45-degree angles and may be transparent for accurate marking of lines. Both are available in metal or durable plastic and may be integrated with measurement scales.

Uses of équerres span measurement, marking, and layout. In carpentry and metalworking, they ensure joints are perpendicular and lines are true. In drafting and architecture, they help transfer right angles from drawings to the workpiece and assist in drawing precise perpendiculars and parallel lines when paired with a ruler or straightedge.

In mathematics and geometry, an équerre denotes a right angle, an angle of 90 degrees, often represented by the symbol ⟂ or by the word angle droit. The concept underpins many geometric constructions and design practices.

See also: right angle, square, set square, carpenter’s square, geometry.