Steel And Tubing Basics:
As general categories, there is tube and pipe. Tube is measured by the outside diameter, while pipe is measured by the inside diameter. In general pipe should not be used on your Jeep. The properties of pipe are very different from tube (pipe has a high carbon content, making it somewhere between cast steel and tubing in strength), and while you can get structural pipe, tube is a better choice for your Jeep projects. Also keep in mind tube and pipe are entirely different so tube can not be bent in a pipe bender, and pipe can not be bent in a tube bended.
For tube, you generally have three choices, HREW, CDEW, and DOM. HREW stands for Hot Rolled Electric Welded, which is tube that is hot rolled, then the seam is welded. You can visually see this seam, although the tube is smooth. CDEW is the same thing except using cold rolled steel. DOM stands for Drawn Over Mandrel. It is sometimes referred to as seamless tubing, but it still has a seam. DOM is made about the same as HREW or CDEW, but after it is welded it is drawn over dies and mandrels under pressure. DOM is generally about 30% stronger than a similar sized piece of HREW. Most people choose to use HREW for most projects as DOM is generally twice the price of HREW. If you use properly sized HREW there's nothing wrong with using it for a roll cage, however, if using DOM you can generally choose a slightly thinner material still achieve the same strength, and be lighter.
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