Hi, i found below websites which manufacturer supiriour quality of pipe fittings which are mainly use for car parts please check below..
http://www.rajendrafittings.com/ or http://www.kalikundsteel.com/ and http://www.gurugautam.com/
Hi..you can check all the specification like thikness, strenth of round tubes please check reffer below reff..
http://www.pipestubings.com or http://www.buyflanges.com and http://www.aluminiumtraders.com