Straight Pipe Thread

Is there any National Pipe Thread Straight (non-tapered, requires O-ring or compression olive) that is compatible, even loosely, with a machine thread threaded rod? I want to put a reducer on the end of a pipe threaded with NPTS and reduce to like 1/4 inch NPTS nominal and have that reducer ride on a 5/16-18 threaded rod. So it’s like a shoring jack or lolly column, but really cheap, and the threaded rod can fit through a small clearance and guide the end of the pipe to the bearing point.