Also known as mild steel, low-carbon steel is easy to machine, form, and weld. These tubes are often fabricated into parts that don’t require high strength, such as frames, supports, and raceways.

Made from 4130 alloy steel, also known as chrome-moly steel, these tubes have low carbon content for good weldability. They’re often used for building frames and supports, since their flat sides make them easier to bolt than round tubes.