floyd (02/17/83)
The "bead" around the edge of a record disc is the added thickness around the outside (it just happens to be rounded). It's purpose is to protect the first few grooves (or instances of the one groove) from being damaged during pressing and packaging.
jwb (02/17/83)
The bead is also there because the manufacturers are making them so damn thin that they wouldn't have and rigidity otherwise.