The quick disconect on a coolant line (I think it is a bypass hose) cracked and broke in the engine. I bought the (special) tool to extract the rest from the hole, but when I hammered the tool in ( like the directions said) it just crumbled and did not bite it well enough to extract it. Now I need to tap the threads but can't tell what size tap I need. The hole is 1/2" and I think pipe thread, but not sure. How is the best way to use the tap, tap in lightly? Thankyou very much for your input and time.