Torx developed by Camcar Textron

Textron

Textron is a conglomerate that includes Bell Helicopter, E-Z-GO, Cessna Aircraft Company, and Greenlee, among others. It was founded by Royal Little in 1923 as the Special Yarns Company, and is headquartered at the Textron Tower in Providence, Rhode Island, United States.With total revenues of...

, is the trademark for a type of screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

 head characterized by a 6-point star-shaped pattern. People who are 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

International Organization for Standardization

The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 as ISO 10664. Torx Plus is an improved profile.

By design, Torx head screws resist cam-out

Cam out

To cam out is a process by which a screwdriver slips out of the head of a screw being driven once the torque required to turn the screw exceeds a certain amount....

 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

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

-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 automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s, motorcycle

Motorcycle

A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s, bicycle brake systems

Bicycle brake systems

A bicycle brake is used to slow down or stop a bicycle. There have been various types of brake used throughout history, and several are still in use today...

, hard disk drives, computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 systems and consumer electronics

Consumer electronics

Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...

. 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. 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. Only the proper driver can drive a specific head size without risk of damaging 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

Size	Inch point to point [in]	Metric point to point [mm]	Maximum torque range [ft-lb]	Maximum torque range [N-m]
T1	.031	.81	.015 to .022	.02 to .03
T2	.036	.93	.051 to .066	.07 to .09
T3	.046	1.10	.103 to .133	.14 to .18
T4	.050	1.28	.162 to .207	.22 to .28
T5	.055	1.42	.317 to .376	.43 to .51
T6	.066	1.70	.553 to .664	.75 to .9
T7	.078	1.99	1.03 to 1.25	1.4 to 1.7
T8	.090	2.31	1.62 to 1.92	2.2 to 2.6
T9	.098	2.50	2.07 to 2.51	2.8 to 3.4
T10	.107	2.74	2.73 to 3.32	3.7 to 4.5
T15	.128	3.27	4.72 to 5.68	6.4 to 7.7
T20	.151	3.86	7.74 to 9.37	10.5 to 12.7
T25	.173	4.43	11.7 to 14.0	15.9 to 19
T27	.195	4.99	16.6 to 19.8	22.5 to 26.9
T30	.216	5.52	22.9 to 27.6	31.1 to 37.4
T40	.260	6.65	39.9 to 48.0	54.1 to 65.1
T45	.305	7.74	63.4 to 76.1	86 to 103.2
T50	.349	8.86	97.4 to 117	132 to 158
T55	.444	11.21	161 to 189	218 to 256
T60	.519	13.25	N/A	379 to 445
T70	.610	15.51	N/A	630 to 700
T80	.690	17.54	N/A	943 to 1048
T90	.784	19.92	N/A	1334 to 1483
T100	.871	22.13	1359 to 1511	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. 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.
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