Square

A square is a hand tool used to mark and verify 90° (right) angles. It consists of a straight blade and a thicker handle (called the stock or beam) set at exactly 90° to each other. By pressing the stock against the edge of a workpiece, you can draw a line across the face that is perfectly perpendicular to that edge.

Types

• Try square: Has a fixed blade riveted to a stock at exactly 90°. Used to check that surfaces are square and to mark cut lines. The blade is thin enough to lie flat on a board while the stock registers against the edge.
• Combination square: A versatile tool with a sliding head that can be locked at any point along a graduated blade. The head includes a 90° face, a 45° face, a spirit level, and a scribe. It measures, marks, and checks square and mitre angles.
• Speed square (rafter square): A triangular tool used primarily in roofing and framing. It combines a fence, a protractor scale, and common-rafter markings in one compact tool.
• Engineer’s square: A precision-ground steel tool with a blade and stock at exactly 90°, used in metalwork and engineering to check squareness to fine tolerances.
• Framing square: A large L-shaped steel rule used in carpentry for laying out rafters, stairs, and framing. The long arm (blade) is 24 inches; the short arm (tongue) is 16 inches.

Why 90° matters

A right angle is the foundation of most construction and woodworking. If the first joint in a project is not square, every subsequent joint compounds the error. Checking for square at every step — with a try square, combination square, or framing square — is one of the most basic quality habits in any trade.