Unable to make revolve cut

Hi

I'm trying to model a piece of magnet with a through hole:

5pcs-15-x-3mm-Hole-4mm-N50-font-b-Magnets-b-font-Strong-font-b-Ring.jpg

However, I'm unable t make a revolve cut:

Does anyone know why the triangle can't be used for a revolve cut?

Thanks

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