Series 3 2.6 6 cyl hose?

Hi Folks, quick query, any one know what the proper name or part number for this hose is, marked with the red arrow (the actual arrow on the picture, not those fast stunt planes...), I have searched on the other posts, promise, but can't find it. Mine has just spilt after a recent head gasket replacement, I must have given it too much grief during the work
Its on a 1979, 2.6 6 cylinder series 3.
cheers
Pete