Mm-mm ...wonder if painting sailing rigging is where the name "rigger brush" came from.
Rigger brushes (sometimes called stripers) are intended for this exact purpose. They are round brushes that come to a point but are much longer than conventional round brushes. They are used for just such a purpose because they do two things:
~ The hold more pigment than regular round brushes.
~ The minimize any handshake that may occur.
I doubt that a ruling pen would be very effective with oil paints. To use a ruling pen the viscosity of the color needs to be quite thin... about the consistency of light cream or whole milk. Even watercolors need to be thinned down and sometimes have ox gall added to make them work well.