A closed end 1/2 lug nut for aluminum wheels fits perfect inside a short piece of heater hose...looks a little funny but doesn't fail...
I tapped the ones on the Duster...maybe 1/4" NPT? definitely check to see if you also need to drill it 1st with a bit for the correct thread...Don't force the tap as the aluminum is thin...Maybe a little grease to capture any shavings...
If I had to do over again I would have cut them off closer to the housing and then tapped them...More like the way the cast water pump fittings install in the bottom pic...