Rain Cap
A conical cap that runs to a point, as over a flue or a vent, with or without a skirt round its rim: the sector it is rolled from. A conical cap that runs to a point, as over a flue or a vent, with or without an upright skirt round its rim: the sector it is rolled from, and the skirt.
How the rain cap is developed, with a worked example · Cones