Carbon Steel Square Tubing 4in x 3/16in x 36in - Structural Grade

Our review looks at the OnlineMetals A500/A513 carbon steel square tubing and finds it best suited for builders and fabricators who need a straightforward, structural-grade stick of steel. The bottom line: this 4 in square tube with a 3/16 in wall and 36 in length delivers solid rigidity and easy modification, making it a practical choice for machine supports, frames, and hobbyist metalwork where a durable, recyclable material is required.

Key Features

• High-strength carbon steel: Provides dependable structural integrity for frames, supports, and load-bearing assemblies.
• 4 in height, 3/16 in wall: The wall thickness balances weight and stiffness for common fabrication tasks without excessive bulk.
• 36 in length: A ready-to-use 3 ft section that fits many workshop projects and reduces cutting time for common layouts.
• Uncoated and modifiable: Ships raw so it can be welded, drilled, cut, or otherwise altered to match design requirements.
• Durable and recyclable: Engineered to resist wear with long service life while remaining recyclable at end of use.
• Multipurpose utility: Works with standard tube connectors and fittings for machine fab, model builds, and separator systems.

Who It's For

This tubing is aimed at tradespeople, engineers, and serious hobbyists who need a dependable, structural steel section for load-bearing or fabricated parts. Its 3/16 in wall and 4 in profile suit small to medium frames, jigs, and machine supports where stiffness and the ability to weld or bolt are key.

Those who prioritize a ready-to-finish surface for painting or decorative use should plan for surface treatment after purchase, and anyone requiring stainless-grade corrosion resistance or precision-ground surfaces for aesthetics should consider alternative materials designed specifically for those needs.

Pros & Cons

Pros

• Good structural strength for frames and supports given the 3/16 in wall thickness.
• Ready for modification: welds, drills, and cuts cleanly for custom projects.
• Practical 36 in length fits many shop layouts and reduces waste from oversize stock.

Cons

• Uncoated finish can show surface rust in some environments, so exterior use may need protection.

Specifications

Material	Carbon steel (A500/A513), ASTM A-36
Shape	Square tubing
Height	4 in
Wall thickness	3/16 in
Length	36 in
Finish	Hot rolled, uncoated

Our Verdict

The OnlineMetals carbon steel square tubing is a solid, no-nonsense choice for fabricators who need a 4 in by 3/16 in structural member in a 36 in length. It offers flexibility for welding and machining, sensible durability, and good value for functional projects; just plan on surface protection if corrosion resistance is important for your application.

Frequently Asked Questions

Can this tubing be welded?
Yes. The hot-rolled carbon steel is suitable for common welding processes and can be welded for structural joints.

Does it come coated to prevent rust?
No. It is supplied uncoated, so exterior or wet-environment use should include a rust-prevention finish or paint.

Is the length exact 36 in?
Yes. The product is sold as a 36 in stick, which is convenient for many shop applications and reduces initial cutting.