These Agilent Varian HS-16 diffusion pump jet coupling part, is part of the jet assembly and is a OEM Agilent Varian replacement part for the HS-16 diffusion vacuum pump. See referenced on Page 40 in instruction manual PDF below. These are original OEM Agilent Varian replacement parts for the HS-16 diffusion pump having part number L6367301, see item #4 in the diagram exploded view & parts illustration below.