Fit them "dry" first to get a feel of how much play is there and then build up the PTFE to suit, adding more thickness as you go down the threads. May need quite a bit as both threads are parallel, not tapered.
Personally I prefer loctite thread for this.
I believe the plastic adapters have a metal thread internally that screws on to the unit. So these should be ok. I can use loctite cord and not really worry about cross threading. Is the top of these that are a male thread in plastic. And I need to connect to 2 x 1/2 female to 15mm compressions
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