a device for blow molding or stretch - blow molding containers from thermoplastic preforms . the device comprises a book mold and actuating means for opening and closing the two pivotable mold halves , including a movable arm freely rotatable about an axis and secured to the two mold halves , and drive means synchronized with the feed rate of the preforms into the mold and designed to actuate guide means having a cam and a cam follower for moving the arm to control the opening and closing of the mold .