This the the helmet of the Black Knight from Monty Python and the Holy Grail. It was designed for my Halloween costume. Print the test print first. It only has one perimeter with a 0.4mm line width and has a 2 mm band at the top and bottom for structure.

Inner Diameter of 210 mm

Link to Black Knight Sword:
https://www.thingiverse.com/thing:6267576