Hi Gagakev a word of caution
If you are using a Carbon Fibre flag pole you could find it splitting on the bottom edge. I presume the pole sits over the head of the bolt and rests on the plate over the nut.
I make and fly kites using a lot of carbon fibre tubing and suffer a lot from split ends
. You will find that if there is pressure on the pole causing a lever action between the bolt head and the nut on the base against the pole the carbon tube will split either at the bottom on the nut or where the bolt head is in contact with the tube. (It does not take much pressure) It would be best to support it by using tubing inside probably the same length as the bolt that is a very close fit to give support over a larger area.
Just a note - The reason carbon fibre flag poles do not split when you use long ground stake for support is that the leverage fulcrum distance is a lot greater so there is less leverage.