A notch that rounds the V notch.Used when stacking trees.
A notch used for intersections when stacking trees crosswise.
By fitting the groove, you can sit better.
In bushcraft, it is sometimes used to cross wood.
It is often used when assembling logs in a log house.
How to make
It is easier to cut if you are conscious of rotating your wrist.
If you are not used to it, try practicing the V notch first.