Combination square

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title: "Combination square" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["dimensional-instruments", "woodworking-measuring-instruments", "metalworking-measuring-instruments", "woodworking-hand-tools", "american-inventions", "squares-(tool)"] description: "Measuring and marking tool" topic_path: "geography/united-states" source: "https://en.wikipedia.org/wiki/Combination_square" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Measuring and marking tool ::

Uses

As well as being used as a regular standalone rule or straightedge, the rule is used in combination with the different heads.

Standard head

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/8c/Combination_square_standard_head_diagram.png" caption="Labelled diagram of the standard head"] ::

The standard head can be used as a:

• Square, for marking and referencing 90° angles and checking if surfaces are flat and square to one another.
• Mitre square, for marking and referencing 45° angles, such as in woodworking for mitre joints.
• Spirit level, to check if a surface is level or similarly if a surface or edge is plumb (vertical).
• Depth gauge or height gauge.
• Form of marking gauge for marking lines parallel to an edge, by setting the head to a certain distance from the end of the rule.
• Reference for directly transferring dimensions without needing to take a measurement, minimising measurement errors and inaccuracies.

Protractor head

::figure[src="https://upload.wikimedia.org/wikipedia/commons/3/34/Combination_square_protractor_head_diagram.png" caption="Labelled diagram of the protractor head"] ::

The protractor head can be used for:

• Measuring and checking angles between surfaces, edges, and markings.
• Marking angles from an edge
• Directly transferring angles, like a bevel gauge (sliding T gauge), to minimise measurement errors and inaccuracies.
• Measuring and marking angles relative to the horizontal by using the spirit level.

Centre finder head

::figure[src="https://upload.wikimedia.org/wikipedia/commons/3/3e/Combination_square_centre_finder_head_diagram.png" caption="Labelled diagram of the centre finder head with a circle as an example"] ::

The centre finder head can be used for:

• Marking lines through the centre of circular or square objects, such as dowels. Making multiple marks at different angles can be used to identify the point at the centre of the circle.
• Marking lines perpendicular to a curved edge (normal lines).
• Bisecting square corners to mark a 45° angle.

History

Though some earlier 19th century tools were called combination squares, the modern combination square was invented in the late 1870s by American inventor Laroy S. Starrett, and patented in 1879. In 1880 he founded the L. S. Starrett Company in Athol, Massachusetts, United States. The tool was originally designed for machinists, but over time became commonly used in other trades, such as woodworking.

Notes

References

References

1. Dotson, Connie. (2015). "Fundamentals of Dimensional Metrology". [[Cengage Learning]].
2. Raghavendra, N. V.. (2013). "Engineering metrology and measurements". [[Oxford University Press]].
3. Campbell, Paul D. Q.. (1995). "An Introduction to Measuration and Calibration". [[Industrial Press, Inc.
4. (2013-02-11). "The Repair of Vehicle Bodies". [[Routledge]].
5. Rae, Andy. (March 2015). "The Multitalented Combination Square: A whole lot of tool in one small package".
6. Capotosto, Rosario. (September 1988). "Combination Square Know-How".
7. (2020-04-25). "Combination Squares".
8. "US Patent: 215,024 - Try Square".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::