Unless you are being funny about the word 'nipple', we are talking about the same type. Look at the left heater pipe in this pic - just above the EGR tube you can see it coming off of the heater core pipe. It's a long 'nipple' but a nipple nonetheless. When I deleted all my coolant lines @ the plenum, these were left open and I didn't realize it until start up. I think they lead to that tube that runs a couple inches through the casting of the plenum and on to more stuff under the plenum. You probably don't have to delete it but I did, and forgot about it because it's not in any write up I saw.