tubing heads are mainly used for oil and gas production to control pressure and ... oil (gas) well; It is also api Casing head, for connection of casing to various wellhead assemblies, is applicable to ... the annual space between the casings, provide crossover connections for installations of BOP, tubing head and tree and other ... of which is flanged API 6B or API 6BX.20", 13 3/8" , 9 5/8" , 7" ,5 1/2" ...