Allen, I am going to wing this answer while waiting for my students to change into their welding gear.
Two general sizes of mandrels, 7 and 10 (I think)mm. Nope, don't need new mandrel unless the ID of the bushings call for it. Then if you want, you can order only the shaft/axle of the mandrel and get the larger one.
I mark the center of my pen blank so I can put it on the mandrel and keep it in the direction it came off of the blank. This way any grain lines or spalting lines will match up on both sides of the center band. For drilling, I put an X on the end of each blank on the center end. This insures your grain lines matching at the center band (where the eye looks for this to occur). If the drill bit wanders off center but not out the side, you will never know once it is turned. I have found a pair of pliers works best for me. I also have a pair of 1/2 X 1/2 inch sticks that I have notches cut in of different sizes that I hold the blank with. But mainly pliers so I can visually check if it is leaning or not. Let's see, did this cover it for you? If not feel free to ask for clarification or more questions.
God and family, the rest is icing on the cake.
I'm so far behind, I think I'm in first place.
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