Ive been searching the net and thats all I can think it is. Theres a sensor/wire that goes before the cat and then theres one actualy on the cat at the back. Ive got a cat replacement pipe but no hole for it to go into. The manufacture said theyd put it in but I need the thread size (this is a secondary o2 sensor isnt it?). Please help Ive been trying to sort this out for over a montha nd dont know whoi to ask as its an import