Every time you audition you fill out a sheet with all your sizes -- sometimes two or three times. When you get called back, you fill out the sheet all over again. When you get booked? The wardrobe person calls you. And asks you yet again for all your sizes.
Maybe they do this because so many people lie about this stuff. More likely it's just plain inefficiency. But I've filled out my size sheets, literally, hundreds of times. It would be cool if, when you sign in at an audition, they could just take your name then print out your little registration sheet, all filled in already with all this info. I don't know. It's a little thing, but it's a pain.
And I still have no idea what my hat size is.