A set square or triangle (
American English
American English, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lang ...
) is an object used in engineering and
technical drawing
Technical drawing, drafting or drawing, is the act and discipline of composing drawings that visually communicate how something functions or is constructed.
Technical drawing is essential for communicating ideas in industry and engineering. ...
, with the aim of providing a
straightedge at a
right angle or other particular planar angle to a
baseline.
Types
The simplest form of set square is a triangular piece of transparent
plastic
Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
(or formerly of polished wood) with the centre removed. More commonly the set square bears the markings of a
ruler
A ruler, sometimes called a rule, scale, line gauge, or metre/meter stick, is an instrument used to make length measurements, whereby a length is read from a series of markings called "rules" along an edge of the device. Usually, the instr ...
and a half circle
protractor. The outer edges are typically
bevelled. These set squares come in two usual forms, both
right triangles: one with 90-45-45 degree angles, the other with 30-60-90 degree angles. Combining the two forms by placing the
hypotenuses together will also yield 15° and 75° angles. They are often purchased in packs with
protractors and
compasses.
Less commonly found is the adjustable set square. Here, the body of the object is cut in half and rejoined with a
hinge marked with angles. Adjustment to the marked angle will produce any desired angle up to a maximum of 180°.
In some European countries a common form of set square combines a 90-45-45 triangle, a ruler and a protractor into a single tool made of stiff or slightly flexible transparent plastic.
Being a mandatory tool used by pupils in
middle school
Middle school, also known as intermediate school, junior high school, junior secondary school, or lower secondary school, is an educational stage between primary school and secondary school.
Afghanistan
In Afghanistan, middle school includes g ...
and higher in German-speaking and neighbouring countries, this specific design is named "" (short form of "", meaning "geometry triangle") or similar.
It was originally developed in 1964 by the German manufacturer (after several refirmations now ''Geotec Schul- und Bürowaren GmbH'').
Relatively uncommon in English-speaking countries, this is sometimes called a "protractor triangle", a term, however, also used for other similar designs. The original design has a hypotenuse length of 15.8 cm and features a 2×7 cm symmetry scale in
millimeter and
degree raster.
Variants in larger sizes, with fixed or detachable handles, with or without bevelled edges (facets), and with or without ink nodules or embossed labels exist as well. Some variants have extra markings at angles of 7° and 42° (138° and 173°) in addition to the normal 45° and 90° markings to ease
dimetric axonometry per ISO 5456-3,
others feature angle scales in
gons instead of degrees. Several other somewhat similar designs named "" ("TZ triangle") exist for (larger) technical drawings (TZ from German: ). The scale reaches from 10 to 10 cm, or even 11 to 11 cm.
Navigation protractor triangles
Similar to the , a number of other protractor triangle types exist for
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
purposes. Various designs are named navigation (protractor) triangle, nautical navigational triangle, nautical set square, Portland (navigational) triangle or Portland protractor triangle, Kent-type triangle, Inoue-type A/B nautical triangle or plotting triangle, course triangle, yachtsmen triangle, and supporting triangle.
However, some widely used navigational protractors, such as the
Cras protractor, are not triangles.
See also
*
Speed square
*
Technical drawing tool
References
{{Authority control
Technical drawing tools
Hand tools
Squares (tool)