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Types of Screws

Modern screws employ a wide variety of drive designs, each requiring a different kind of tool to drive in or extracting them. The most commonly used screw drives are the slotted and Phillips; hex, Robertson, and torx which are also common in some applications. Some types of drivers are intended for automatic assembly in mass-production of such items as automobiles. More exotic screw drivers types may be used in situations where tampering is undesirable, such as in electronic appliances that should not be serviced by the home repairperson.

Different types:

Slot head is a single slot, and is driven by a flat-bladed screwdriver. The slotted screw is common in the woodworking applications, but is not often seen in applications where a power driver would be used, due to the tendency of a power driver to slip out of the head and potentially damage the surrounding material.

Cross-head, cross-point or Phillips screw has a "+"-shaped slot and is driven by a cross-head screwdriver, designed originally for use with mechanical screwing machines. The Phillips screw drive has slightly rounded corners in the tool recess, and was designed so the driver will slip out, or cam out, under strain to prevent over-tightening.

Pozidriver is patented, similar to cross-head but designed not to slip, or cam out. It has four additional points of contact, and does not have the rounded corners that the Phillips screw driver has. Phillips screwdrivers will usually work in Pozidriv screws, but Pozidriv screwdrivers are likely to slip or tear out the screw head when used in Phillips screws. Pozidriv was jointly patented by the Phillips Screw Company and American Screw Company.

Torx is a star-shaped or splined bit with six rounded points. These were found in early Apple Macintosh computers, to discourage home repairs.

Hexagonal or hex screw head has a hexagonal hole and is driven by a hexagonal wrench, sometimes called an Allen key, or by a power tool with a hexagonal bit.

Square-drive head is an American clone of the Robertson that has a square hole without taper. Due to the lack of taper, the hole must oversize relative to the screwdriver, and is much more likely to strip than the Robertson.

Tri-Wing screws have a triangular slotted configuration. They are for instance used by Nintendo on its Game Boys to discourage home repair.

Torq-Set is an uncommon screw drive that may be confused with Phillips; however, the four legs of the contact area are offset in this drive type.

Spanner drive uses two round holes opposite each other, and is designed to prevent tampering. Commonly seen in elevators in the United States.

Keep in mind that the rubber handles on screw drivers are for comfort and grip. They aren't designed to protect the user from electrical shock. If you must work on the live electrical equipment, be sure that your screw driver has an insulated handle and a nonconducting shaft.