The steel thread rolling screw for use in plastic has a black oxide finish and an 82-degree flat head with a star drive. Steel is often used in applications where strength is the primary consideration. The black oxide finish offers mild corrosion resistance and lubricity. The flat head has an 82-degree cone-shaped bearing surface for use in countersunk holes and a flat top that fits flush with the mated surface. The star drive, also called a Torx drive, has a six-pointed indentation that provides a large contact area for the driver, resisting slippage better than a Phillips or slotted drive. A star drive requires use of a Torx driver for installation and removal.
Thread cutting and thread rolling screws, two types of self-tapping screws, are threaded fasteners that create a mating thread in the wall of a hole. The two screws differ from each other in the way that they create the threads. Thread cutting screws cut the wall of the hole to create the thread, creating material chips that need to be cleared away from the hole to prevent clogging. Thread rolling screws, also called thread forming screws, do not remove material but instead press against the wall of the hole to displace the material and form the threads.