I have book called 'the few' and it is about certain pilots who fought in the battle of britain. It includes letters and memorabilia of the pilots in the book, and it is a limited edition copy. It's quite large, and blue in colour. Anyway, it includes pictures of one pilots headgear set (which he said was special to him) and it is a c-type with a pop-stud in the middle. I wonder what it's for though?