Torx

Torx (pronounced /tɔːrks/) is a trademark for a type of screw drive characterized by a 6-point star-shaped pattern, developed in 1967[1] by Camcar Textron.

Initially, they were sometimes used in applications requiring tamper resistance, since the drive systems and screwdrivers were not widely available.

Rather than rely on the tool to slip out of the screw head when a desired torque level is reached (which risks damage to the driver tip, screw head, or workpiece), torque-limiting driver designs achieve a desired torque consistently.

Because the plane of contact is not perpendicular to this circle, a radial force is also generated which tends to "burst" the female component and "crush" the male one.

The magnitude of this force is proportional to the cotangent of the angle (depicted in orange) between the green circle and the contact plane.

For the Torx type of design, the angle is much closer to 90° than in the case of the hex head, and so for a given torque the potentially damaging radial force is much lower.

The same series of Torx drivers is used to drive SAE, metric and other thread system fasteners, reducing the number of bit sizes required.

The "external" variants of Torx head sizes (see below) are described using the capital letter "E" followed by a number ranging from E4 to E44.

However, the pin allows a smaller flat head screw driver to be used successfully between two adjacent lobes.

AW drive is a hexalobular-type screw head similar to Torx, with a tapered profile to aid in centering, developed by the Würth Group in Germany.

[31] T-Star plus has a similar screw drive design to Torx ttap and was introduced in 2005 by German fastener manufacturer Altenloh, Brinck & Co under its brand name Spax.