Technically yes..
I use a black sharpie to mark the blank in the middle prior to drilling, glueing the tubes and mounting on the lathe.
Once the tubes are glued in (squared and cleaned out.) I put a little line mark on the inside if the tube corresponding with the mark I put on prior to drilling and gluing. Again using a sharpie. And yes the tip will go inside a 7mm tube..
I never mark the wood after the initial mark that will get turned off..
If that makes sense... If not then I'm lost also..