Interesting name, huh? I'd guess it has something to do with the size of lead singer DeeDee O'Malley's head - just a guess. Size7Hat is a band formed by four Scientologists (all of whom I know - does that make me famous?) Anyway their first CD is out and can be bought at various locations such as www.cdbaby/cd/size7hat and Size7Hat at Tower Records.
There is a little tidbit about them at: Size7Hat. By-the-way, the cover for the CD ("The Outside") is brilliant.