Editing Combination square

{{Short description|Measuring and marking tool}}
{{Use dmy dates|date=October 2023}}{{Infobox tool|name=Combination square|caption=A Starrett combination square with a standard head|classification={{unbulleted list|Hand tool|[[Square (tool)|Type of square]]}}|image=Combination square.jpg|other_name={{unbulleted list|Combo square|Adjustable square|Sliding square}}|inventor=[[Laroy S. Starrett]] (1877)}}A '''combination square''' is a multi-purpose measuring and marking tool used in [[metalworking]], [[woodworking]], and [[stonemasonry]]. It is composed of a [[Ruler|rule]] and one or more interchangeable heads that can be attached to the rule.<ref name=":4">{{Cite book |last=Dotson |first=Connie |url=https://books.google.com/books?id=qCpBBAAAQBAJ |title=Fundamentals of Dimensional Metrology |publisher=[[Cengage Learning]] |year=2015 |isbn=978-1305177741 |pages=100–106}}</ref><ref name=":3">{{Cite book |last=Raghavendra, N. V. |url= |title=Engineering metrology and measurements |publisher=[[Oxford University Press]] |others=Krishnamurthy, L. |year=2013 |isbn=978-1-68015-280-7 |location=New Delhi |pages=89–91 |oclc=900729269}}</ref> Other names for the tool include '''adjustable square''', '''combo square''', and '''sliding square.'''

The most common head is the standard head, which is used as a [[Square (tool)|square]] for marking and testing 90° and 45° angles.<ref>{{cite book |last=Campbell |first=Paul D. Q. |title=An Introduction to Measuration and Calibration |publisher=[[Industrial Press, Inc|Industrial Press Inc]] |year=1995 |isbn=978-0-8311-3060-2}}</ref> The other common types of head are the protractor head, and the centre finder head.<ref name=":1">{{Cite book|last1=Livesey|first1=Andrew|url=https://books.google.com/books?id=54grhsUcM3gC&q=%22combination+square%22&pg=PT122|title=The Repair of Vehicle Bodies|last2=Robinson|first2=A.|date=2013-02-11|publisher=[[Routledge]]|isbn=978-1-135-12049-8|edition=6th|pages=93|language=en}}</ref>

== Description ==
[[File:CombinationSquareSet.jpg|thumb|A combination set with the rule (top), a standard head (left), protractor head (centre), and a centre finder head (right).]][[File:Illustration_of_a_combination_square.png|thumb|280x280px|Illustration showing a centre head, protractor head, and standard head attached to a rule.]]
=== Rule ===
Combination square rules are made of steel and can be purchased with gradations in [[Metric system|metric]], [[Imperial units|imperial]], or both metric and imperial. Both faces of the rule have markings, providing four different sets of markings. This allows different sides to have different graduations (eg. 1mm or 0.5mm markings) or units (ie. metric and imperial). The rule typically comes in lengths between 150mm and 600mm or between 4 inches and 24 inches.<ref name=":4" /><ref name=":3" />

=== Heads ===
The heads, occasionally called anvils, are attached to the rule by sliding the rule into a slot in the side of the head. The head is then tightened in place via a lock bolt or lock nut which engages with a channel running the full length of the rule, allowing the head to be tightened on at any point along the rule.<ref name=":1" /><ref name=":3" />

The standard or square head has three adjacent flat faces, two of them meet square to one another, and the third face is angled away at 45°. When attached one face is parallel to the rule, one face is perpendicular, and one face is at 45°. The standard head usually incorporates a small spirit level and a small removable [[scriber]].<ref name=":1" />

The protractor head has a flat reference edge which is attached to an adjustable 180° [[protractor]] or (sometimes called a turret) with a graduated scale in both directions for reading both the angle or the complement angle.<ref name=":4" /> The protractor head sometimes includes a small spirit level.<ref name=":1" /><ref name=":3" />

The centre finder head has two faces meeting at 90°, when attached one edge of the rule [[Bisection|bisects]] the two faces at 45°.

The heads are manufactured from either forged steel, cast iron, die-cast aluminium, die-cast zinc, or plastic. Aluminium and zinc heads are cheaper than steel and iron, but less durable and more prone to inaccuracy.<ref>{{Cite magazine|last=Rae|first=Andy|date=March 2015|title=The Multitalented Combination Square: A whole lot of tool in one small package|url=https://www.woodcraft.com/blog_entries/the-multitalented-combination-square-a-whole-lot-of-tool-in-one-small-package|magazine=Woodcraft Magazine|pages=50–54|issn=1553-2461}}</ref> Cast iron and steel heads are also notably heavier. The heads are usually painted except for the flat machined reference faces.{{Citation needed|date=October 2020}}

== 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 ===
[[File:Combination_square_standard_head_diagram.png|thumb|280x280px|Labelled diagram of the standard head]]
The standard head can be used as a:

* [[Square (tool)|Square]], for marking and referencing 90° angles and checking if surfaces are flat and square to one another.
* [[Miter square|Mitre square]], for marking and referencing 45° angles, such as in woodworking for [[Miter joint|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.<ref>{{Cite magazine |last=Capotosto |first=Rosario |date=September 1988 |title=Combination Square Know-How |url=https://books.google.com/books?id=zOQDAAAAMBAJ&q=%22combination+square%22&pg=PA130 |magazine=[[Popular Mechanics]] |page=130 |issn=0032-4558 |access-date=25 October 2020}}</ref>
* Reference for directly transferring dimensions without needing to take a measurement, minimising measurement errors and inaccuracies.<ref name=":0">{{Cite web |date=2020-04-25 |title=Combination Squares |url=https://www.popularwoodworking.com/techniques/combination-squares/ |access-date=2020-10-24 |website=[[Popular Woodworking Magazine]] |language=en-US}}</ref>

=== Protractor head ===
[[File:Combination_square_protractor_head_diagram.png|thumb|280x280px|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 [[Sliding T bevel|bevel gauge]] (sliding T gauge), to minimise measurement errors and inaccuracies.
* Measuring and marking angles relative to the horizontal by using the spirit level.<ref name=":3" />

=== Centre finder head ===
[[File:Combination_square_centre_finder_head_diagram.png|thumb|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 [[Dowel|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 (geometry)|normal lines]]).
* [[Bisection|Bisecting]] square corners to mark a 45° angle.<ref name=":3" />

== 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.{{efn|Sources differ on the exact year he invented the tool, but the US patent was filed and granted in 1879.|name=|group=note}}<ref>{{Cite web|title=US Patent: 215,024 - Try Square|url=http://www.datamp.org/patents/displayPatent.php?pn=215024&id=17915|access-date=2020-10-24|website=Directory of American Tool and Machinery Patents}}</ref>  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.<ref name=":0" />

== Notes ==
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== References ==
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