The SCCA allows only four materials for roll bar construction: seamless, DOM and ERW mild steel and chrome moly. Seamless tubing is produced using a process that is similar to forging. It has a refined grain structure and has a slight spiral twist for added strength. Drawn Over Mandrel (D.O.M.) tubing is made from steel strips and welded together. It is then cold drawn down to a smaller diameter and thinner wall to give it more strength. Electric Resistance Welded (ERW) tubing is made by rolling flat steel into a tube and welding it together. It is easily identifiable by the short flashing on the inside of the tube.

Any of these materials are usable, but ERW tubing needs to be thicker than the others for the same strength. Mild steel is available in many types depending on the metals it is made from. Some are stronger, while others are easier to form. The SCCA requires roll bar or cage material to be SAE 1010, 1020 or 1025. Due to its greater strength, chrome moly (SAE 4125 or 4130) can be thinner than mild steel but is much harder to weld properly. It must be "normalized" after welding, which involves heating and slowly cooling the entire structure in a specialized oven. If this is not done weld embrittlement can weaken the structure.

Some racecars have been built with stainless steel or aluminum roll bars, but these are highly specialized (and expensive). They are often not allowed in amateur racing due to the difficulty of welding and normalizing them, which can lead to failure even if the welds look good to the naked eye. Mild steel is actually the best material as it is easy to weld properly (by a professional) and does not require treating before use.

The diameter and wall thickness of your bar will be determined by the weight of your car. A good starting point is 1.5 inches in diameter x .120 wall for cars under 1,500 pounds; alloy (chrome moly) could be 1.375 x .090 wall. For 1,500 to 2,500 pound cars 1.75 x .120 (mild) or 1.625 x .102 (alloy). For cars over 2,500 pounds consider 2.25 x .120 (mild) or 2.00 x .102 (alloy).

Roll cages can use smaller tubes since a cage is a stronger structure. For under 1,500 pounds, tubing could be 1.375 inches x .095 (mild) or 1.375 x .080 (alloy). For 1,500 to 2,500 pounds the SCCA requires 1.5 x .095 (mild) or 1.375 x .095 (alloy). Over 2,500 pounds required 1.50 x .120 (mild) or 1.50 x .095 (alloy). These dimensions are for properly designed and triangulated cages. If you are planning for a more basic cage, then stronger tubing would be appropriate. Some other clubs require a 3/16-inch inspection hole be drilled in a non-stressed portion of the bar, so tech inspectors can verify the wall thickness.

* The front cage had to withstand a load of 3.5w daN (w = vehicle weight + 150kg) applied to the top of the windscreen at an angle of 25 deg x 5 deg (+/- 1 deg). (Reference drawing No. 253 - 38B)

* The complete roll cage must withstand a vertical load of 7.5w daN (w = weight of the car + 150 kg) applied on the top of the main roll hoop. (Reference drawing No. 253 - 38B)

* The door aperture had to have a vertical member if the distance between initial downwards bend and the final mounting exceeds 200mm. (Reference drawing No. 253 - 4)

* The 'B' post hoop required two diagonal members in it, as well as being gusseted in the centre.(Reference drawing No. 253 - 4)

* The roof above the driver/ co-driver had to have two cross members in it. For competitions without co-drivers, only one diagonal member had to be fitted but its front connection had to be on the driver's side. (Reference drawing No. 253 - 9)

* The actual certification had to be carried out by an institutionalised test house independent to the manufacturer.