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Torx (pronounced "tor-x") developed^[when?] by Camcar Textron,^[1] is the trademark for a type of screw head characterized by a 6-point star-shaped pattern. 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 standardized by the International Organization for Standardization as ISO 10664.^[2] Torx Plus is an improved profile.

By design, Torx head screws resist cam-out better than Phillips head or slot head 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. The manufacturer claims this can increase tool bit life by ten times or more.

Torx screws are commonly found on automobiles, motorcycles, bicycle brake systems, hard disk drives, computer systems and consumer electronics. Initially, they were sometimes 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.^[3] Today, Torx screws are also becoming increasingly popular in construction industries.

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.^[4] 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.

The "external" variant of Torx head sizes (see below) are described using the capital letter "E", followed by a number.

Properties of various Torx drives^[5]
Size	Inch point to point [in]	Metric point to point [mm]	Maximum torque range [N-m]
T1	.031	.81	.02 to .03
T2	.036	.93	.07 to .09
T6	.066	1.70	.75 to .9
T7	.078	1.99	1.4 to 1.7
T8	.090	2.31	2.2 to 2.6
T9	.098	2.50	2.8 to 3.4
T10	.107	2.74	3.7 to 4.5
T15	.128	3.27	6.4 to 7.7
T20	.151	3.86	10.5 to 12.7
T25	.173	4.43	15.9 to 19
T27	.195	4.99	22.5 to 26.9
T30	.216	5.52	31.1 to 37.4
T40	.260	6.65	54.1 to 65.1
T45	.305	7.74	86 to 103.2
T50	.349	8.86	132 to 158
T55	.444	11.21	218 to 256
T100	.871	22.13	1843 to 2048

Variants

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.

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, introduced about 1990 when the original Torx patent was expiring, is designed to allow greater torque, and to minimize wear.^[6] The specifications for these licenses 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 TX".

A tamper resistant version of Torx Plus exists, 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 TS".

Competitive variants

TTAP, which is also hexalobular, is designed to minimize wobbling without the need for magnetic bits, a feature that can be important to certain industrial users. 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.

Gallery

Torx bits T15, T20, T25 and T30
A Torx wrench
closeup of Torx bit

References

^ Camcar eventually became part of Textron Fastening Systems in the 1990s. In 2006 Textron Fastening Systems was sold to Platinum Equities, LLC, of Beverly Hills, California. They renamed the company Acument Global Technologies, which as of 2010 includes Avdel, Camcar, Ring Screw, and others.
^ ISO 10664 http://www.iso.org/iso/catalogue_detail.htm?csnumber=40257
^ "Fast and Secure," Feature Article, June 2005
^ Chart of Torx fasteners and tools
^ Wiha TORX Dimensional & Screw size Specifications
^ "Torx Plus drive system" (pdf). Acument.

[1] Camcar eventually became part of Textron Fastening Systems in the 1990s. In 2006 Textron Fastening Systems was sold to Platinum Equities, LLC, of Beverly Hills, California. They renamed the company Acument Global Technologies, which as of 2010 includes Avdel, Camcar, Ring Screw, and others.

[2] ISO 10664 http://www.iso.org/iso/catalogue_detail.htm?csnumber=40257

[3] "Fast and Secure," Feature Article, June 2005

[4] Chart of Torx fasteners and tools

[5] Wiha TORX Dimensional & Screw size Specifications

[6] "Torx Plus drive system" (pdf). Acument.

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 {{Screws}}
-'''Torx''' (pronounced "torks") developed{{When|date=February 2011}} by Camcar [[Textron]],<ref>Camcar eventually became part of Textron Fastening Systems in the 1990s. In 2006 Textron Fastening Systems was sold to Platinum Equities, LLC, of Beverly Hills, California. They renamed the company [http://www.acument.com/ Acument Global Technologies], which as of 2010 includes Avdel, Camcar, Ring Screw, and others.</ref> is the trademark for a type of [[screw]] head characterized by a 6-point star-shaped pattern. 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 standardized by the [[International Organization for Standardization]] as  '''ISO 10664'''.<ref>ISO 10664 http://www.iso.org/iso/catalogue_detail.htm?csnumber=40257</ref> '''Torx Plus''' is an improved profile.
+'''Torx''' (pronounced "tor-x") developed{{When|date=February 2011}} by Camcar [[Textron]],<ref>Camcar eventually became part of Textron Fastening Systems in the 1990s. In 2006 Textron Fastening Systems was sold to Platinum Equities, LLC, of Beverly Hills, California. They renamed the company [http://www.acument.com/ Acument Global Technologies], which as of 2010 includes Avdel, Camcar, Ring Screw, and others.</ref> is the trademark for a type of [[screw]] head characterized by a 6-point star-shaped pattern. 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 standardized by the [[International Organization for Standardization]] as  '''ISO 10664'''.<ref>ISO 10664 http://www.iso.org/iso/catalogue_detail.htm?csnumber=40257</ref> '''Torx Plus''' is an improved profile.
 By design, Torx head screws resist [[cam out|cam-out]] better than [[Phillips head]] or [[slot head]] 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.  The manufacturer claims this can increase tool bit life by ten times or more.