This is the longer type cylinder head adaptor tube which allows fitment of the by pass hose without removing the head. The shortened hose
GZA2083 slides up the tube and then back down on the water pump tube. Frequently rusted on old heads and not even there on newer heads. These are 5/8"uns x 16tpi "whitworth fine" thread and if the thread in the head is badly corroded and you cannot find the correct original tap some owners have used 5/8" x 18tpi unf thread tap and fitted
12H1405MS tube originally used for inlet manifold servo take offs.