I think the flex is more suitable for all the occasion 。 especially the <a href="http://www.newerahatfactory.com/fox-racing-caps-c-107.html"> fox racing hats</a>,they are awesome cool.
they measure the head of the consumer. pretty sure it is around the forehead and how 'thick' you're head is, depends what kind of hat you are getting. :] get a top hat.