Torx screws and drive bits are available in 24 sizes, labeled "T1" through "T100," and measure between 0.031 and 0.871 inches from one point to another. This six-pointed style, commonly known as a star bit, is also referred to as hexalobular.
Torx also features sockets and nut drivers used with external head bolts. These are labeled "E4" through "E24," and measure between 0.15 and 0.87 inches from point to point.
This style of screws, bits and sockets was developed by the Camcar Company in response to other, more conventional screw head types that could only handle limited torque before stripping. Torx styles eliminate this weakness.