On one of my benches is a pile of instructions to assemble pens ,heaps of sheets of them everyone saying do this then that in this order. Well the brass parts all fit into and the meat ie the finished timber or acrylic should meet together at that size. Always check the bushes,they should fit snug in the brass. Now if they are the right size outside when you turn the blank it will be almost level with the shoulders on the bushes. Thats why there are bushes.
!. they support the blank on the mandrel.
2. They enable the pen to be made.
3. there are other methods.
Now comes the crunch,meticulous labelling of the containers for bushes if you want an easy flow of production.
Every kit has a need,so think carefully when you buy different kits.
Peter.