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Extrusion Terminology

Standard shape

Extrusions available to all customers.

Exclusive shape

Extrusions manufactured to client design and produced for their exclusive use. These are not published in our catalogue.


Alloys, tempers, dimensions and services always available and acceptable without further reference.


Alloys, tempers, dimensions and services which are outside normal availability and always the subject of special inquiry.

Section drawings

Profile outline drawings prepared for every extruded shape. Each one is identified by a die number (e.g. UA 1234)

Visible Face

In a finished construction, the visible surface of any extrusion.

External periphery

The measurement used in computing the price for surface finishes on hollow shapes in which the external perimeter only is measured, and the internal void excluded.

Total periphery

The total distance around the extruded shape, including internal void surfaces.


Result of dividing the total perimeter (internal and external for hollow shapes) of the section in millimetres by weight in kg/m.

Circumscribing circle

Minimum circle inside which the extruded shapes fit precisely.

Thickness ratio

Optimum desirable ratio of variation of metal thickness in any extruded shape.


Solid round section, 10 mm or greater in diameter whose length is great in relation to its diameter.


Solid section, long in relation to its cross-sectional dimensions, with a symmetrical square, rectangular, hexagonal, or octagonal cross-section (excluding flattened wire) with sharp or rounded corners or edges and whose width or greatest distance between parallel faces is 10 mm or greater.

Solid Shape

Extruded shape whose geometry does not form a void and which is long in relation to its cross-sectional dimensions.

Hollow Shape

Single enclosed void with a width to depth ratio of not less than 5:1. Wall thickness should be uniform except for radiused corners.

Semi-hollow Shape

Solid shape with a cross-section that partially encloses a void, in which the area of the void is substantially greater than the square of the width of the gap, otherwise classified as a hollow as follows.

Gap Dimensions

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