For Classic racing cars we have to use 40 x 2,0mm or 38 (1,5") x 2,5mm (0.25") , and are alowed to fix it to the shell at 6 point by bolting or welding , but there is one exeption , when we fit the V bars into the main hoop we are allowed to use two extra points on the transmission tunnel ,That also means No welding or bolting to the pillars and roofsides .