A star screwdriver is a handheld tool with a six sided, star shaped bit. It is designed to interact specifically with star screw heads that are sized to match corresponding bits exactly. This type of screwdriver prevents cam out during use, while creating an ideal amount of torque between screws and the project work area.
This type of driver was invented by the company Textron. This company also performs work in the automotive, aviation, and software industries through a variety of smaller businesses. It was patented under the name Torx® for its ability to achieve perfect torque without slipping, though most individuals refer to this design as a star based on its visual appearance.
The primary benefit of using a star screwdriver is that it resists the urge to cam out during use. The term cam out is used to refer to the action created when a screwdriver or drill bit pops out of the screw head indentations while turning. Some driver heads, such as the Philips head, are designed to cam out intentionally to prevent the user from damaging the screw head or bit once the maximum amount of torque needed has been reached between a screw and a stationary object. Consequently, as the bit rotates in the head when using a power drill, it can strip and wear down the grooves in the screw, making it impossible to back it out later if necessary.
The unique design of the star screwdriver features a six pointed star shape at the tip. This tip fits precisely into a similarly sized screw head. Sizes are designated by the letter T followed by a number, where larger numbers correspond to bigger drivers. As the driver turns, each point of the star bites against the solid surface of the screw head, preventing slippage or camming out. The driver consistently provides the same amount of torque to each screw to which it is applied, stopping when maximum torque has been reached.
The star screwdriver and screw head were initially created for precision work on computer equipment and sensitive avionics controls. It then became popularized in the automotive and construction industries as well. Tamper resistant versions of this style of head are also available to provide an added level of security on some devices due to the difficulty of obtaining the specific matching driver. These star heads often include a circular post cut out that requires a specialty bit, or use a five sided rather than six sided design.