Screw Head Types
TORX, developed by Textron in the USA, is the trademark name for a type of screw head with a 6-point star shaped pattern. As such they are often referred to as 'star drive' heads, although they have a rather grand generic name: hexalobular internal driving feature.
TORX head screws are designed to resist cam out better than Phillips, PZD and slotted screws. Whereas Phillips heads were designed tocause the driver to cam out to prevent over-tightening, TORX heads were designed to prevent it.
The reason for this was the development of better torque-limiting automatic screwdrivers for use in factories. Rather than relying on the tool slipping out of the screw head when a torque level is reached, and thereby risking damage to the driver tip, screw head and work piece, the drivers themselves were designed to consistently achieve a desired torque. It is claimed that this can increase tool bit life by ten times or more.
TORX screws are commonly found on cars, computer systems (Compaq uses almost exclusively T15 screws) and consumer electronics, but are also becoming increasingly popular in construction.
Tamper Proof TORX
A version known as Tamper Proof TORX has a host in the centre of the screw head that stops a standard TORX driver from being used. Where a standard TORX screw can be turned with a slotted screwdriver of the right size, it's not possible with a Security TORX.
Modulo screws are a combination of slotted and cross head designs. they are most commonly found in electrical equipment.
Slotted and PZD screwdrivers can be used on these screws, however there is a strong possibility that either the screw or the screwdriver will be damaged.
Perhaps even more importantly, there is a risk that the screw is not adequately tightened, potentially dangerous when working with electricity.