A combination square is a multi-purpose measuring and marking tool used in

metalworking Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale ...

woodworking Woodworking is the skill of making items from wood, and includes cabinet making (cabinetry and furniture), wood carving, joinery, carpentry, and woodturning. History Along with stone, clay and animal parts, wood was one of the first mate ...

, and

stonemasonry Stonemasonry or stonecraft is the creation of buildings, structures, and sculpture using stone as the primary material. It is one of the oldest activities and professions in human history. Many of the long-lasting, ancient shelters, temples, ...

. It is composed of a

rule Rule or ruling may refer to: Education * Royal University of Law and Economics (RULE), a university in Cambodia Human activity * The exercise of political or personal control by someone with authority or power * Business rule, a rule pert ...

and one or more interchangeable heads that can be attached to the rule. 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 for marking and testing 90° and 45° angles. The other common types of head are the protractor head, and the centre finder head.

Description

Rule

Combination square rules are made of steel and can be purchased with gradations in

metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathe ...

imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas ...

, 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.

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. 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 A scriber is a hand tool used in metal work to mark lines on workpieces, prior to machining. The process of using a scriber is called scribing and is just part of the process of marking out. It is used instead of pencils or ink lines, because t ...

. The protractor head has a flat reference edge which is attached to an adjustable 180°

protractor A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two sw ...

or (sometimes called a turret) with a graduated scale in both directions for reading both the angle or the complement angle. The protractor head sometimes includes a small spirit level. The centre finder head has two faces meeting at 90°, when attached one edge of the rule 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. Cast iron and steel heads are also notably heavier. The heads are usually painted except for the flat machined reference faces.

Uses

As well as being used as a regular standalone rule or

straightedge A straightedge or straight edge is a tool used for drawing straight lines, or checking their straightness. If it has equally spaced markings along its length, it is usually called a ruler. Straightedges are used in the automotive service and m ...

, the rule is used in combination with the different heads.

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 A marking gauge, also known as a scratch gauge, is used in woodworking and metalworking to marking out, mark out lines for cutting or other operations. The purpose of the gauge is to scribe a line parallel to a reference edge or surface. It is us ...

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

The

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

The centre finder head can be used for: * Marking lines through the centre of circular or square objects, such as

dowels A dowel is a cylindrical rod, usually made of wood, plastic, or metal. In its original manufactured form, a dowel is called a ''dowel rod''. Dowel rods are often cut into short lengths called dowel pins. Dowels are commonly used as structural ...

. 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 The L. S. Starrett Company () is an American manufacturer of tools and instruments used by machinists, tool and die makers, and the construction industry. The company was founded by businessman and inventor Laroy Sunderland Starrett in 1880. ...

, and patented in 1879. In 1880 he founded the L. S. Starrett Company in

Athol, Massachusetts Athol is a town in Worcester County, Massachusetts, United States. The population was 11,945 at the 2020 census. History Originally called Pequoiag when settled by Native Americans, the area was subsequently settled by five families in Sept ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. The tool was originally designed for machinists, but over time became commonly used in other trades, such as woodworking.

Notes

References

{{Authority control Dimensional instruments Woodworking measuring instruments Metalworking measuring instruments Woodworking hand tools American inventions Squares (tool)