For BSF I would suggest buying the brass ones a size larger, running the threaded portion on a lathe to the appropriate size, then running them into a die. You likely won't get the threads to bottom out, but that should give a good sealing interference fit. A jeweller's lathe could be used to cut the threads if need be. Seems like a lot of work for the fittings, but an afternoon on the lathe should make up as many as one would need for a project like this.
Very possibly the brass fittings will be buffed/polished before installation. The artillery likes those kinds of things.
|