I suspect one specifically cut for working brass. I checked through a copy of an old Nicholson publication I have and they show one similar with what they call “a short upcut” in that the teeth are cut at a more shallow angle. See here…
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This is a great little book, by the way, for anyone who loves knowing the why’s and how’s of the tools we use. Can’t remember where I sourced it but you may be able to track it down. If not let me know and we’ll figure something out.
-frank
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