I have 2 Grey Fox Helmets, $30 each ( I pay the shipping ). Here's the dimensions, one of the helmets was miscut on one side, the other one just needs the paint job redone.
The dimensions of the helmets are 31" Circumfrence around the middle of the helmet to allow for padding and electronics (not included).
17" Circumfrence around the neck opening.
From Chin to eye level is 5" high.
From Chin to the top of the helmet is about 10.5" high.
From the back of the helmet to the top is about 9" high.