A combination square is a multi-purpose measuring and marking tool used in metalworking, woodworking, and stonemasonry. It is composed of a rule and one or more interchangeable heads that can be attached to the rule. The tool is also known by the names 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
thumb|A combination set with the rule (top), a standard head (left), protractor head (centre), and a centre finder head (right).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, 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. 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, the rule is used in combination with the different heads.
Standard head
thumb|280x280px|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
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 bevel gauge (sliding T gauge), to minimise measurement errors and inaccuracies.
- Measuring and marking angles relative to the horizontal by using the spirit level. 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.