Here's a tip for filing the flats on ramrod pipes.
First, clamp the pipe by the tab and file the bottom flat. I don't measure or mark the width of the flat. I just count my file strokes when making my first cuts with a course file. Make the same number of strokes on each flat.
I leave the tabs extra tall and drill a small hole at the top. Screw the tab to a piece of scrap wood to hold the pipe for filing the side flats.
Last, clamp the pipe to the oblique flat of a barrel. This places the oblique flats horizontal for filing.