HSS, RHS, SHS and CHS terminology

Steel hollow sections are described with several abbreviations that depend partly on market and standards culture.

The most common are:

• HSS — Hollow Structural Section;
• RHS — Rectangular Hollow Section;
• SHS — Square Hollow Section;
• CHS — Circular Hollow Section.

The key point is that HSS is usually an umbrella term, especially in North American practice, while RHS, SHS and CHS describe the cross-sectional shape more explicitly.

HSS in North American practice

AISC uses HSS for structural hollow sections and distinguishes:

• rectangular HSS;
• square HSS;
• round HSS.

For example, AISC notes that rectangular and square HSS are designated by outside dimensions and wall thickness, while round HSS use outside diameter and wall thickness.

So an American drawing may simply say “HSS” where a European MTO would more often say RHS, SHS or CHS.

RHS, SHS and CHS

In European/international steel trading:

RHS

Rectangular Hollow Section

Example format:

RHS 200 × 100 × 10 mm

SHS

Square Hollow Section

Example:

SHS 100 × 100 × 8 mm

CHS

Circular Hollow Section

Example:

CHS 168.3 × 8 mm

The exact available size series and tolerances depend on the product standard and manufacturer.

Is SHS technically also an RHS?

Geometrically, a square is a special rectangle.

Commercially, steel catalogues normally separate SHS and RHS because the naming is useful for procurement and stock classification.

Do not collapse the terms when copying an MTO.

HSS is not automatically “pipe”

This is particularly important for round products.

A round HSS/CHS can share the same outside diameter and wall thickness as a pipe product, but the product standard and intended use can be different.

AISC specifically distinguishes round structural HSS call-outs from ASTM A53 pipe designations.

The same issue exists in Europe:

• structural hollow sections commonly fall under standards such as EN 10210 or EN 10219;
• pressure/line/mechanical tubes use different product standards.

See Which EN tube standard applies?.

HSS does not tell you hot-finished or cold-formed

The abbreviation HSS tells you the product is a structural hollow section. It does not, by itself, tell you the manufacturing/delivery route.

In Europe, EN 10210 vs EN 10219 is the more useful distinction:

• EN 10210 covers hot-finished structural hollow sections and allows both seamless and welded routes within scope;
• EN 10219 covers cold-formed welded structural hollow sections.

Therefore a complete procurement description needs more than “HSS.”

What should appear in an RFQ?

A good hollow-section line item normally identifies:

• CHS / RHS / SHS or HSS shape;
• outside dimensions;
• wall thickness;
• length;
• material grade;
• product standard;
• delivery condition where applicable;
• certificate type;
• any special testing/tolerance requirements.

For example:

RHS 200 × 100 × 10, S355J2H, EN 10210, EN 10204 3.1

is much more procurement-ready than:

HSS 200 × 100

MetalMate takeaway

HSS is the broad structural-hollow-section term; RHS, SHS and CHS identify rectangular, square and circular shapes. Never infer the governing standard, manufacturing route or grade from the abbreviation alone.

Related Knowledge

• EN 10210 vs EN 10219
• Which EN tube standard applies?

References

• AISC, HSS Solutions Center / HSS designation guidance: https://www.aisc.org/aisc/solutions-center/hss/
• AISC, Mill production and tolerances — round HSS versus pipe: https://www.aisc.org/aisc/solutions-center/engineering-faqs/1-mill-production-and-tolerances/
• NEN, EN 10210-1:2006: https://www.nen.nl/en/nen-en-10210-1-2006-en-107293
• NEN, EN 10219-1:2006: https://www.nen.nl/en/nen-en-10219-1-2006-en-107340