Most of the threading done on pens is still done with tap and dies, Not that you cant do it on a lathe, but the length of the threads is so short that its easier to use a tap and die rather than change the gears and use a hand wheel. The micro mark 7 x 16 is a favorite and so is the jet 9 x 20. If you go witha used lathe, make sure you know what to look for on a lathe that could be a problem or take someone along that does. Nothing like buying a lathe to find out its more repairs and money than its worth.