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An assortment of Torx driver bits.
A Torx-8 screw on a hard drive.
Part of the series on
Screw drive types
 
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Slotted (flat or straight)
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Phillips ("crosshead")
PH
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Pozidriv (SupaDriv)
PZ
 
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Square
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Robertson (square)
 
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Hex
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Hex socket (Allen)
 
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Torx
T, TS, TX
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Tri-Wing
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Torq-set
 
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Spanner head
(Snake-eye)
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Triple square
XZN
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Polydrive
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One-way - Clutch
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Spline drive
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Double hex
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Bristol

TORX (pronounced "TORKS", rhyming with "forks"), developed by Camcar LLC of Acument Global Technologies (formerly Camcar Textron), is the trademark for a type of screw head characterized by a 6-point star-shaped pattern (in the same way that slotted heads, Phillips, hex socket, and Robertson have linear, cruciform, hexagonal, and square tips, respectively). People unfamiliar with the trademark generally use the term star, as in star screwdriver or star bits. The generic name is hexalobular internal driving feature and is standardised by the International Organization for Standardization as ISO 10664. TORX is frequently styled Torx despite the official all-caps trademark styling.

By design, TORX head screws resist cam-out better than Phillips head or slot head (flathead) screws. Where Phillips heads were designed to cause the driver to cam out, to prevent over-tightening, TORX heads were designed to prevent cam-out. The reason for this was the development of better torque-limiting automatic screwdrivers for use in factories. Rather than rely on the tool slipping out of the screw head when a torque level is reached, thereby risking damage to the driver tip, screw head and workpiece, the driver design achieves a desired torque consistently. Camcar LLC claims this can increase tool bit life by ten times or more. Today there are also other solutions, such as the AW type of screw head developed by the Würth group in Germany.

TORX drive system was developed in the Camcar Technical center, located in Rockford, Illinois, USA.

TORX screws are commonly found on automobiles, bicycle brake systems, hard disk drives, computer systems (Compaq uses almost exclusively T15 screws) and consumer electronics. Initially, they were used in applications requiring tamper-resistance since the drive systems and screwdrivers were not widely available; as drivers became more common, tamper-resistant variants, as described below, were developed.[1] Today, TORX screws are also becoming increasingly popular in construction industries.

Camcar LLC developed an improved profile, designated TORX PLUS.

Contents

Sizing

TORX head sizes are described using the capital letter "T", followed by a number. A smaller number corresponds to a smaller point-to-point dimension of the screw head. Common sizes include T10, T15 and T25, although they reach as high as T100. A sample chart is available here. Only the proper driver can drive a specific head size without risk of ruining the driver or screw. The same series of TORX drivers is used to drive SAE, metric and other thread system fasteners, reducing the number of bit sizes required.

Variants

Security TORX driver
External TORX driver
  • A version known as Security TORX, Tamper-Resistant TORX (often shortened to Torx TR) or pin-in-Torx contains a post in the center of the head that prevents a standard TORX driver (or a straight screwdriver) from being inserted. The design of other security fastener's heads have a "center pin reject" reject, including the security version of the Allen key.
  • An external TORX version exists, where the screw head has the shape of a TORX screwdriver bit, and a special TORX socket is used to drive it, although a standard hex socket can often be used. These are found primarily on automobile engines.
  • A TORX variant, TORX PLUS, is designed to allow greater torque, and to minimize wear. Currently, TORX PLUS heads and drivers are patented, slowing adoption in the marketplace, but is licenced to a number of tool manufacturers [1] including Camcar [2] and Facom [3]. The specifications for these licences are held by Textron. Standard TORX drivers can be used to drive TORX PLUS screws, but not to full torque because of the loose fit. TORX PLUS drivers will not fit standard TORX screws. They are shortened to 'Torx TS'.
  • There is also a tamper resistant version of TORX PLUS, having five lobes rather than six and a solid post in the center. This is used for tamper resistance as the drivers are still hard to obtain, and are given the designation 'Torx TX'.
  • Another variant, TTAP, which is also hexalobular as the original TORX, is designed to allow greater stick-fit, and to minimize the wobbling. Currently, TTAP heads and drivers are patented, slowing adoption in the marketplace. Standard TORX drivers can be used to drive TTAP screws, but TTAP drivers will not fit standard TORX screws. There is also a tamper resistant version of TTAP.
  • TORX screws and screwdrivers with triangle-shaped sockets and heads are used in the Netherlands and cannot be found in North America.

References

External links

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