Written by Jody Muelaner
A Torx screw is a six-lobed, star-drive socket or external head.
A Torx screw is a type of screw characterized by a six-lobed, star-patterned screw drive. Torx drive is a trademark commonly referred to as star drive or, simply, a six-lobe. It’s often abbreviated to TX or 6lobe. The ISO name is hexalobular.
Torx is available as an internal and external drive although it is most commonly used as a socket within the head (internal).
Torx screws were invented in 1967, by Camcar Textron, as an improvement on contemporary drive types. It aimed to replace Phillips, which was prone to cam-out, and the internal hex drive, which tended to fail during high torque by rounding off.
Torx does not cam-out and can withstand higher torques than internal hex at a given head size. Vertical sidewalls maximize tool engagement and produce no cam-out forces to push the driver out of the screw head, resulting in less fatigue as no end load is required. It’s also less likely to damage the driver or driven screw.
With a perpendicular drive angle to the axis of the fastener, Torx drive produces minimal radial force. This force distribution allows a higher torque to be transmitted with little likelihood of reaming of failure — either of the driver or the driven screw.
Torx internal drive screws are typically used within automotive, IT, and consumer electronics manufacturers. They’re also increasingly used in other sectors, such as in building and construction.
The internal head sizes are marked by a capital letter ‘T’ followed by numbers 1 to 100, with smaller numbers representing smaller head sizes. Typical sizes are T10, T15, and T25, with inch and metric sized fasteners sharing the same sized drive tools. An external drive Torx is marked by a capital letter “E,” followed by numbers 4 to 40 (the numbers do not correspond with internal Torx).
The external drive Torx is less common, however, it has gained some popularity in machine screws and lag screws as an alternative drive head type to hex.
Successors to Torx include Torx Plus, which was introduced in the early ’90s. Its squarer lobes promised to increase drive bit life by 12. In 2017, the latest Torx successor, Torx Paralobe, was released, offering 20% greater torsional strength and 20% greater drive life than Torx Plus.
Early uses of Torx included as security screw heads, reliant solely on being an uncommon driver type. However, as the drive gained popularity, other drives were invented to fill this role. One design features a “center pin reject,” known as Security Torx, Tamper-Resistant Torx, or pin-in Torx. It’s abbreviated as TR and has a solid post in the center of the screw socket that prevents a standard driver from entering and requires a specialist hollow-headed driver.
Another security screw design inspired by Torx is the five-lobed star pattern, known as the pentalobe security screw. It’s been featured on Apple products since 2009.
Torx ttap, is a spin-off product promising a magnet free solution to stabilizing the screw on the driver through the use of a second recess in the head matching a pin on the driver.
Filed Under: Screws • nuts • bolts • rivets