I see noone has yet helped you. As I suspect it is possible there are different kinds of things that might be referred to informally or otherwise as a "PVC PLUG ADAPTER" (and for different kinds of purposes/services), you might want to provide just a little more information as to the intent/service for better help. If however the pvc device is female threaded and your e.g. galvanized? bushing has the same outer male threads/diameters, one would think you could indeed at least attempt to turn one into the other.
However, the fact that I think some pvc "adapters/ors" are basically intended for simple low/no pressure cleanouts etc., your "bushing" with a smaller tapped hole in same may be some unsettling, as I believe female-threaded pvc items are notoriously weak and prone to cracking/leaking from healthy torque/assembly on to begin with, let alone subsequent bending load and impacts from say a galvanized pipe? eventually threaded into same!
I had already attached the bushing and the adapter (the female part of a pvc plug). It only went for about a quarter of an inch. Then afterwards I just put sealant.
BTW: im using this kind of fitting for my homemade hydraulic ram. This fitting is seen on the pressure chamber.
