A drum has a shell, a pair of batter heads disposed on two sides of the shell, a pair of collars enclosing the batter heads and surrounding the shell, a pair of positioning hoops surrounding the collars, a large number of connection seats disposed on the shell, a large number of positioning mounts disposed on the positioning hoops, and a large number of positioning fasteners fastening the connection seats and the positioning mounts together. Each of the positioning hoops has an inner curved flange to press the corresponding collar on the shell.