Rapid leak of coolant at thermostat housing

The o-ring on my thermostat housing blew out about 2 days ago I just went ahead and baught a whole new housing and 2 new bolts to mount it but after it is all put back together I have a fast steady leak coming from the metal line that connects to my thermostat housing. Ive gone to 2 auto parts stores and nobody knows what metal line im talking about the o-ring ripped off of it and since they dont know the line then they cant find the right o-ring. Can you please tell me what the line is called.