I don't think you could do the very top part even on a circ that small. If you don't want to use DPNs try using two circular needles of the same needle size. There are videos of how to do it in the advanced techniques section of the videos here.
When asking questions ALWAYS post the name and a link for the pattern if you have it.
You can for a few rows, but the top of a hat ends up being only about 4" around or less. Instead of using a smaller circ or dpns, you can do Half a loop, maybe Magic loop, or use a 24-32" circ for Magic loop, or use 2 circs.
sue- knitting heretic
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