I have made this hat for my brother. I have used circular needles size 4mm, and 4.5mm.
Its pattern raises the problem of changing the flat stitches to circular one again. I have changed many flat stitches to circular stitches, and wandered about the criteria of that changing. Of course there are some of criteria , but also there are some flat stitches cannot be circular. One of that kind of stitches which doesn't change to circular is that one which borrow some of it from previous one.
I changed that one to circular , but found out it is difficult to write the pattern.