This is my thirty plus yr old blank trimmer called those days a step drill,always used by hand for utmost care and precision is guaranteed by the neat fit of the front stem. It carefully cleans the brass end with a champher. This one I use for all my Slimline pens. I enclose some variations of this.Food for thought this was the only device you could buy when I started,most people used it in a hand drill.Too clumsy for me so I handled mine.
If you look back up the page at my 212 inch sander you will see a block of wood with a piece of mandrel set in it that I used to face these blanks,it is held on a square mitre in the bed groove.
Peter.