To install them, put the lower part on the Nitto fitting first, this can take a bit of effort, as it has little lips each end to hold it in place (as much as possible), plus its designed to stretch a little to seal against the nut, and to enlarge the flange, so the top ‘pops’ on.
Then put the retaining ring over the top of the lower part, and then the cap should now go on.
