Hexagonal (hex) socket
Has a hexagonal hole and is driven by a hex wrench, sometimes called an Allen key or Hex key, or by a power tool with a hexagonal bit. Tamper-resistant versions with a pin in the recess are available. Hex sockets are increasingly used for modern bicycle parts because hex wrenches are very light and easily carried tools. They are also frequently used for self-assembled furniture.
Invented in 1908 by Canadian P.L. Robertson, has a square hole and is driven by a special power-tool bit or screwdriver. In the United States it is referred to as square drive. The screw is designed to maximize torque transferred from the driver, and will not slip, or cam out. It is possible to hold a Robertson screw on a driver bit horizontally or even pendant, due to a slight wedge fit. Commonly found in Canada in carpentry and woodworking applications and in Canadian-manufactured electrical wiring items such as receptacles and switch boxes. It is increasingly used in the United States for woodworking applications.
Has a triangular slotted configuration. They have been used by Nintendo on several consoles and accessories, including the Game Boy, Wii, and Wii Remote,and by Nokia on some phones and chargers to discourage home repair, as well as in some pencil sharpeners to prevent removal of the blade.
Torq-Set or offset cruciform
May be confused with Phillips; however, the four legs of the contact area are offset in this drive type. This type is commonly used in the aerospace industry.
Uses two round holes opposite each other, and is designed to prevent tampering. Commonly seen in elevators in the United States. Note that in the UK, "spanner" is the usual word for "wrench".
Clutch Type A or standard clutch
Resembles a bow tie. These were common in GM automobiles, trucks and buses of the 1940s and 1950s, particularly for body panels.
Clutch Type G
Resembles a butterfly. This type of screw head is commonly used in the manufacture of mobile homes and recreational vehicles.
Is a type of tamper-resistant drive that uses a triangular recess in the screw head.
Some screws have heads designed to accommodate more than one kind of driver, sometimes referred to as combo-head or combi-head. The most common of these is a combination of a slotted and Phillips head, often used in attaching knobs to furniture drawer fronts. Because of its prevalence, there are now drivers made specifically for this kind of screw head. Other combinations are a Phillips and Robertson, a Robertson and a slotted, a torx and a slotted, and a triple-drive screw which can take a slotted, Phillips or a Robertson. The Recex drive system claims it offers the combined non-slip convenience of a Robertson drive during production assembly and Phillips for after market serviceability. Quadrex is another Phillips/Robertson drive. Phillips Screw Company offers both Phillips and Pozidriv combo heads with Robertson.
Combined slotted/pozidriv heads are so ubiquitous in electrical switchgear to have earned the nickname 'electricians screws' (the first screwdriver out of the toolbox is used - the user does not have to waste valuable time searching for the correct driver). Their rise to popular use has been in spite of the fact that neither a flat screwdriver or pozidriv screwdriver are fully successful in driving these screws to the required torque. Some screwdriver manufacturers do offer matching screwdrivers and call them 'contactor screwdrivers'. Slotted/philips (as opposed to slotted/pozidriv) heads occur in some North American made switchgear.