Common Sizes of Square Tubes for Automotive Use

What are the Commonly used Sizes of Square Tubes in Automobiles?

Modern automotive mainframes rarely use traditional "square tubes." Instead, they utilize complex closed or open sections formed by stamping and welding steel sheets. However, square tubes and rectangular tubes do find widespread application in specific automotive applications, primarily in commercial vehicles, modified vehicles, and performance vehicles. The size of square tubes in automobiles is entirely determined by design strength, spatial layout, and regulatory requirements, and is therefore customizable.

Introduction to Common Square/Rectangular Tube Sizes in Automotive Use:

The following sizes are a common range, but specific sizes vary depending on the vehicle model, design, and manufacturer.

1. Chassis and Frames for Commercial Vehicles (Trucks, Buses, and Trailers)

These applications require extremely high strength and rigidity, and rectangular tubes made from high-strength low-alloy steels (such as Q345 and Q700) are often used.

Automotive Applications:

Truck Chassis Rails: Rectangular tubes are predominantly used, rather than square tubes. 

Common specifications: 80×50×3.0mm to 120×60×5.0mm

Bus body frames: Mainly used for pillars and waist beams.
Common specifications: 50×50×2.5mm to 100×50×3.0mm

Trailer beams and frames: Key load-bearing components.
Common specifications: 80×40×3.0mm to 120×60×4.0mm

Roll cages (for construction vehicles): Require high strength and bending resistance.
Common specifications: 50×50×2.5mm to 75×75×3.0mm

2. Automotive Interior Structures (passenger cars and commercial vehicles)

This type of application prioritizes lightweighting and formability, often using ordinary carbon steel (Q235) or high-strength steel.

Automotive applications:

Seat frames: Require high dimensional accuracy and surface quality. 

Common Specifications: 25×25×1.5mm to 40×40×2.0mm

Battery Pack Frame (New Energy Vehicles): Mostly made of rectangular tubing, providing support and protection.
Common Specifications: 30×30×2.0mm to 50×50×2.5mm

Bumper Beam (Internal Reinforcement): Used on some models.
Common Specifications: 40×40×2.0mm to 60×60×2.5mm

Roof Rack Rail (Internal Structure)
Common Specifications: 20×20×1.5mm to 30×30×1.5mm

3. Car Modification and Aftermarket

This is the largest application area for square tubing, and dimensions are entirely determined by design requirements.

Roll Cage: CDS (Cold-Drawn Seamless) steel tubing, commonly made of SAE 1020 or 4130 chrome-molybdenum steel. 

Note: International competition standards generally require the use of round tubing, but amateur and circuit racing often utilize square/rectangular tubing for some structural components.

Chassis reinforcements: Customizable upon request.
Off-road vehicle bumpers: Thick walls ensure strength.
Tow hooks/towing arms

4. New Energy Vehicle Battery Pack Trays

This is an emerging and important application area. As a core component of the vehicle body, the battery pack's tray frame utilizes a large number of square and rectangular tubing to form a sturdy grid structure to support and protect the battery cells.

Common specifications: 25×25×1.5mm to 50×50×2.5mm
Material: 6061 and 6063 aluminum alloy square tubing are commonly used for lightweighting; high-strength steel is also an option.

What are the Commonly used Square Tubing Materials in Automobiles?

Automotive square tubing materials range from the lowest-cost carbon steel to high-performance chrome-molybdenum steel and aluminum alloys to meet diverse requirements. Material selection is strictly dependent on the application, performance requirements (strength, weight, corrosion resistance), and cost.

Common Material Grades:
Carbon Steel: Q235, SAE 1020
Features: Low cost, easy to process, average strength.
Applications: Commercial vehicle frames, interior brackets, amateur vehicle modification

High-Strength Steel: Q345B, Q700
Features: High strength, good cost-effectiveness, and strong load-bearing capacity.
Applications: Truck chassis, trailer beams, battery pack frames

Chromium-Molybdenum Steel: SAE 4130
Features: Extremely high strength-to-weight ratio, requires specialized welding.
Applications: Professional racing roll cages, high-performance modification parts

Aluminum Alloy: 6061-T6, 6063, 6082
Features: Extremely light, corrosion-resistant, high cost
Applications: New energy battery packs, lightweight bus bodies

Stainless Steel: 304 / 304L
Features: Excellent corrosion resistance, high cost, low strength

Applications: Special vehicles, high-end decorative parts

Read more: Square Tube Size Chart or Square tube vs. Round tube