Steel hollow sections are used across construction, engineering and fabrication, but choosing the right product involves more than selecting a shape.
Rectangular, square and circular steel tubing each offer different advantages depending on the application. Understanding these differences can help builders, fabricators and purchasing teams select suitable materials, streamline fabrication and avoid unnecessary delays.
Whether you’re sourcing steel for a building frame, equipment support or general fabrication project, knowing what to look for can make the ordering process much easier.
What are steel hollow sections?
Steel hollow sections are tubular products with a hollow interior. They are available in different shapes, sizes, wall thicknesses and grades to suit a wide range of applications.
The three main types are Rectangular Hollow Sections (RHS), Square Hollow Sections (SHS) and Circular Hollow Sections (CHS).
United Steel supplies all three through our steel pipe and tube range, with various sizes, grades and finishes available to suit different project requirements.
Each section has its own characteristics, making it important to understand the differences before placing an order.
RHS: Rectangular Hollow Sections
Rectangular Hollow Sections have four flat sides, with two longer faces and two shorter faces.
Their rectangular shape makes them particularly useful for building frames, structural supports and fabricated components where a specific width or depth is required.
The flat surfaces also provide convenient connection points for welding brackets, plates and other steel components.
RHS is commonly used for:
- Structural framing and supports
- Equipment frames and machinery
- General steel fabrication
- Building and infrastructure projects
The rectangular profile allows engineers to select dimensions that suit the required structural performance and available space.
For fabricators, RHS can also be a practical option when components need to sit flush against a flat surface.
SHS: Square Hollow Sections
Square Hollow Sections have four equal sides, creating a consistent profile that works well across structural and general fabrication applications.
SHS is commonly used for posts, frames, equipment supports and other fabricated structures.
Its square shape provides equal external dimensions in both directions, making it particularly convenient when a consistent profile is required.
Like RHS, the flat faces also make it straightforward to position and connect other components.
Typical applications include:
- Steel posts and support structures
- Fabricated frames
- Machinery and equipment supports
- General construction and manufacturing
SHS is often considered where a square appearance is desirable or where the design calls for equal width and depth.
The final section size and wall thickness should always be selected according to the project’s engineering requirements.
CHS: Circular Hollow Sections
Circular Hollow Sections have a round profile and are commonly used in construction, engineering and architectural applications.
Unlike RHS and SHS, CHS has no flat sides or corners. This can make it particularly useful for exposed steelwork where a smooth, circular appearance is preferred.
Its round shape also provides consistent geometric properties about any axis through its centre, which can be advantageous in certain structural applications.
CHS is commonly used for:
- Structural columns and bracing
- Steel posts and supports
- Architectural steelwork
- General engineering and fabrication
One consideration is that connecting brackets or plates to a curved surface may require different fabrication details from those used with rectangular or square sections.
The most suitable option will depend on the design, connection requirements and intended application.
Understanding steel hollow section sizes
Once you’ve identified the required section type, the next step is confirming the dimensions.
RHS and SHS are generally specified by their external dimensions and nominal wall thickness.
For example, a 100 × 50 × 3 mm RHS has external dimensions of 100 mm by 50 mm and a nominal wall thickness of 3 mm.
CHS is typically specified by its outside diameter and nominal wall thickness.
Wall thickness is particularly important because sections with the same external dimensions can have different weights and structural capacities.
When ordering, check the approved drawings and confirm the required dimensions, thickness and lengths before proceeding.
Choosing the right grade and finish
Steel grade and finish are important considerations when selecting hollow sections.
United Steel supplies tubular products in various grades, including C250L0, C350L0 and C450L0, depending on the product and specification.
Our range also includes painted, primed and galvanised options for different fabrication and corrosion protection requirements.
For structural applications, the specified grade and product should comply with the relevant Australian Standards, including AS/NZS 1163 where applicable.
The right combination of grade, size and finish will depend on the intended use, environment and engineering requirements.
Talk to United Steel about your steel pipe and tube requirements
Choosing between RHS, SHS and CHS starts with understanding your project’s requirements, including the appropriate dimensions, grade and finish.
United Steel supplies a comprehensive range of steel pipe and tube products to customers across Australia, supported by established supplier relationships and steel processing capabilities.
Whether you’re sourcing structural tubing for construction or hollow sections for general fabrication, contact United Steel to discuss your requirements and find the right supply solution for your next project.