Editing Torx (section)

==Principles of operation==
[[File:Torx-hex-contact-angles-forces.svg|thumb|upright|The angle between the plane of contact between tool and fastener and the circumferentially directed force is much closer to 90° in a Torx type of head (lower) than in a conventional [[Hex key|hex]] head (upper). (Exaggerated for illustrational purposes)]]

By design, Torx head screws resist [[cam out]] better than [[Phillips head]] or [[slot head]] screws.<ref name="patent667" /> Whereas the tendency of Phillips drivers to cam out under excessive torque has been listed as a feature preventing damage to the screw-head or driver,<ref>{{cite patent |country=US |number=2474994 }}</ref> Torx heads were designed to ''prevent'' cam-out. The development of better [[Torque limiter|torque-limiting]] automatic screwdrivers for use in factories allowed this change. 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.

The Torx design allows for a higher torque to be exerted than a similarly sized conventional hex socket head without damaging the head or the tool.<ref name="patent667" /> The diagram depicts the interaction between the male and female components of a conventional hex drive and a Torx drive. The clearance between the components is exaggerated for clarity.

The green circle, passing through the six points of contact between the two components, represents the direction of the rotational force being exerted at each of those points. 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. If this radial force component is too great for the material to withstand, it will cause the corners to be rounded off one or both components or will split the sides of the female part. 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. This property allows the head of the fastener to be smaller for the same required torque, which can be an advantage in applications where space to accommodate the head is limited.