What Is a Machinist Square?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 02 December 2019
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A machinist square is a tool used by metalworkers to confirm that projects are properly aligned. It is very similar to the try square used in woodworking to test 90° angles in the process of preparing projects and producing finished work. Manufacturers typically produce sets of squares of different sizes to allow metalworkers to select the most appropriate for a given project. They are usually made from sturdy, non-corrosive metals so they can be used in a variety of work environments.

The design includes a base and a blade set at a 90° angle. There may be a small notch at the base to prevent accumulations of debris that could throw off the measurements. To use the machinist square, a metalworker aligns the base with the project and checks the blade against the component that is supposed to be at a right angle. If a gap is present, it indicates that the angle is not perfect, and the project needs some adjustment.


This equipment is extremely precise, with very small tolerances for error. It is designed for use in complex metalworking projects where getting the angles accurate is critical, as an error could create serious problems with operation and function. The machinist square typically has several pins to hold the blade on, and the machinist can test it for accuracy using a set of discs. Four discs can be laid out in the inner angle of the square to create a grid. A ruler can be used to measure the end-to-end points to confirm the angle is accurate.

A machinist square can be used for other projects where right angles are of critical concern. The tool can be used to check an existing angle for squareness, or to adjust components of a project to create a perfect right angle. It is important to store machinist squares in a safe location where they are unlikely to be strained. Over time, pushing and pulling forces can change the angle, making it less accurate. Periodic calibration can help technicians identify and correct problems.

Tool size can be an important consideration when selecting a tool to work with. Larger squares can be more cumbersome and may be harder to handle. Small ones are ideal for small projects, but do not provide enough accuracy for large items. A little square can be used to machine something like a tool, for example, while someone preparing a large metal frame needs a big machinist square to make sure the angle is straight all the way up.


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