Internal threads are commonly found on plastic parts that screw together, such as bottle caps, drinkware lids and plastic hardware. Due to the delicate nature of threads, molding these parts requires a slightly different approach than your average plastic part. An unscrewing core must be incorporated in the tool in order to eject them from the mold without damaging the threads.
In order to actuate the rotating cores, different drive systems can be incorporated and the action is coordinated with the press cycle so that your internally threaded parts occur when the mold is opened.