Lee, I actually cheated a little on this one. I body portion of the pen is an El Grande complete with threaded nib assembly. The cap portion mounted on the base is made with the Gentlemen's brass tube and Gentlemen's Gold TN centerband. The black innersleeve was replaced with a plastic sleeve turned down to fit the interior of the brass tube where I tapped threads to accomidate the pen body. Since I didn't want the pen to screw down into the cap portion, I threaded only enough for the pen body to "catch" the threads to hold it in place. The lower portion of the cap end has a 7mm brass tube to accept the swivel funnel piece.