From my Samples, Singulars, and Somethings Completely Different collection -

A 14 gauge kettle helm made by GDFB for European export. Their helmet sizing for the US is size Large and size Medium - (I guess they think we have fat heads) - I have one available that is a size Small. My head is 22 3/4", and when I try it on this touches at the front and back (of my bascinet shaped skull). See measurements below:

outer circumference: 27"
inside liner circumference: 23 1/2"
inside liner, front to back: 8"
inside liner, side to side: 7"
weight: 4 lb 13.0 oz