Square tubes are lightweight, thin-walled steel pipes with a hollow square cross-section, also known as cold-formed steel sections. They are formed by cold bending steel strip or coil, which is then heat- or cold-rolled, and subsequently high-frequency welded to achieve the desired square cross-section dimensions. In addition to the increased wall thickness, hot-rolled extra-thick-walled square tubes also feature corner dimensions and edge straightness that meet or exceed those of resistance-welded cold-formed square tubes.

By Process Classification
Square tubes are categorized by production processes: hot-rolled seamless square tubes, cold drawn seamless square tubes, extruded seamless square tubes, and welded square tubes.

Among the welded steel tubes, there are further classifications:
(a) By process: Arc Welded Square Tubes, Resistance Welded Square Tubes (High Frequency, Low Frequency), Gas Welded Square Tubes, Furnace Welded Square Tubes
(b) Seam-welded sections – Straight seam square pipes, Spiral seam square pipes

By Material Classification
Square tubes are categorized by material, including plain carbon steel square tubes and low-alloy square tubes. Plain carbon steel includes grades such as Q195, Q215, Q235, SS400, 20# steel, and 45# steel; low-alloy steel includes grades such as Q345, 16Mn, Q390, ST52-3, etc.

Categorized by production standards
Square tubes are categorized according to production standards: National Standard Square Tubes, Japanese Standard Square Tubes, British Standard Square Tubes, American Standard Square Tubes, European Standard Square Tubes, and Non-standard Square Tubes.

By cross-sectional shape classification
Square tubes are classified by their cross-sectional shape:
Simple Section Square Pipe - Square Tube, Rectangular Tube
(2) Complex Cross-Section Square Tubes - Flower-shaped Square Tubes, Open-mouthed Square Tubes, Wavy Square Tubes, and Special-shaped Square Tubes

Surface Treatment Classification
Square tubes, categorized by surface treatment: Hot-dipped galvanized square tubes, Electroplated zinc square tubes, Oiled square tubes, and Pickled square tubes.

By Application Type
Square tubes categorized by application — Decorative square tubes, Machine tool equipment square tubes, Mechanical industry square tubes, Chemical industry square tubes, Steel structure square tubes, Shipbuilding square tubes, Automotive square tubes, Steel beam column square tubes, Special purpose square tubes

Categorized by wall thickness
Square tubes are categorized by wall thickness into ultra-thick-walled, thick-walled, and thin-walled tubes.