This is the tutorial from youtube to make the bolt pen. If you have a metal lathe you don't need to use the file. I made part of mine differently to the tutorial as I found something that didn't look right to me so I did it my way. It's in approx 6 parts.
Peter
https://www.youtube.com/watch?v=WWWUhq1R0kI
Peter
https://www.youtube.com/watch?v=WWWUhq1R0kI