Torx (pronounced /tɔːrks/), developed in 1967[1] by Camcar Textron,[2] is the trademark for a type of screw head characterized by a 6-point star-shaped pattern. A popular generic name for the drive is star, as in star screwdriver or star bits. The official generic name, standardized by the International Organization for Standardization as ISO 10664, is hexalobular internal.[3] This is sometimes abbreviated in databases and catalogs as 6lobe (starting with the numeral 6, not the capital letter, G). Torx Plus is an improved head profile.

Torx screws are commonly found on automobiles, motorcycles, bicycle brake systems (disc brakes), 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.[4] Torx screws are also becoming increasingly popular in construction industries.

Torx screw
A Torx T8 screw on a hard disk drive.
T6 screw screw driver.jpeg
T6 screw driver

Principles of operation

The angle between the plane of contact between tool and fastener and the circumferentially directed force is much closer to 90º in a Torx type of head (lower) than in a conventional hex head (upper).

By design, Torx head screws resist cam-out better than Phillips head or slot head screws.[1] 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,[5] Torx heads were designed to prevent cam-out. The development of better 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, and/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 and/or the tool.[1] 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 90º 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.

The disadvantage on older Torx heads is that the smaller internal "splines" can corrode relatively easily and cause the Torx driver to slip and damage the head, making it more difficult to remove than the traditional hexagon head.


Torx head sizes are described using the capital letter "T" followed by a number ranging from T1 to T100.[6] A smaller number corresponds to a smaller point-to-point dimension of the screw head (diameter of circle circumscribed on the cross-section of the tip of the screw driver). Common sizes include T10, T15, and T25, while T5.5, T35, and T47 tend to see specialized use. 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" variants of Torx head sizes (see below) are described using the capital letter "E" followed by a number ranging from E4 to E44.[7] The "E" numbers are different from the "T" numbers of the same size: for example, an E4 Torx socket fits a T20 head.[6]

Properties of various Torx drives[6]
Size Point-to-point distance Maximum torque range ~ E Torx
(in) (mm) (lb·ft) (N·m)
T1 0.031 0.81 0.01–0.02 0.02–0.03
T2 0.036 0.93 0.05–0.07 0.07–0.09
T3 0.046 1.10 0.10–0.13 0.14–0.18
T4 0.050 1.28 0.16–0.21 0.22–0.28
T5 0.055 1.42 0.32–0.38 0.43–0.51 E2
T6 0.066 1.70 0.55–0.66 0.75–0.90
T7 0.078 1.99 1.0–1.3 1.4–1.7
T8 0.090 2.31 1.6–1.9 2.2–2.6
T9 0.098 2.50 2.1–2.5 2.8–3.4
T10 0.107 2.74 2.7–3.3 3.7–4.5
T15 0.128 3.27 4.7–5.7 6.4–7.7
T20 0.151 3.86 7.74–9.37 10.5–12.7 E4
T25 0.173 4.43 11.7–14.0 15.9–19 E5
T27 0.195 4.99 16.6–19.8 22.5–26.9
T30 0.216 5.52 22.9–27.6 31.1–37.4 E6
T35[9] E7
T40 0.260 6.65 39.9–48.0 54.1–65.1 E8
T45 0.306 7.82 63.4–76.1 86–103.2
T47[10][11] GM-Style
T50 0.346 8.83 97.4–117 132–158 E10
T55 0.440 11.22 161–189 218–256 E12
T60 0.519 13.25 280–328 379–445 E16
T70 0.610 15.51 465–516 630–700 E18
T80 0.690 17.54 696–773 943–1048 E20
T90 0.784 19.92 984–1094 1334–1483
T100 0.871 22.13 1359–1511 1843–2048 E24


Torx driver secure
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.
  • An External Torx version exists, where the screw head has the shape of a Torx screwdriver bit, and a Torx socket is used to drive it. The external “E” Torx nominal sizing does not correlate to the “T” size, (e.g. an E40 socket is too large to fit a T40 Torx bit, while an E8 Torx socket will fit a T40 Torx bit[6]).
Properties of various External Torx drives
Size   Point-to-point distance [6]    Standard fastener selection [7] 
(in) (mm) SAE Metric
E4 0.15 3.8 #6 M3
E5 0.18 4.7 #8 M4
E6 0.22 5.6 #10 M5
E7 0.24 6.1
E8 0.29 7.4 1/4" M6 & M7
E10 0.36 9.3 5/16" M8
E12 0.43 11.1 3/8" M10 & M11
E14 0.50 12.8 7/16" M12
E16 0.57 14.7 1/2"
E18 0.65 16.6 9/16" M14
E20 0.72 18.4 5/8" M16
E24 0.87 22.1 3/4" M18 & M20
E28 7/8" M22
E32 1" M24 & M27
E36 1-1/8" M30
E40 1-1/4" M33
E44 1-3/8" M36
  • A Torx successor, Torx Plus, was introduced about 1990 when the original Torx patent was expiring. The lobes are more square to allow for higher torque and to minimize wear. The name is shortened to IP (Internal Plus) with sizes ranging from 1IP to 100IP [12] (sometimes listed as IP1 to IP100 [13]) and EP (External Plus) with sizes ranging from 1EP to 42EP as well as smaller sizes ranging from H7EP to H2EP and includes five-lobed tamper-resistant variants.[12] 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 into standard Torx screws.
    • A tamper-resistant version of Torx Plus exists having five lobes rather than six, plus a solid post in the center, and is used for security as the drivers are uncommon.[14] Though Acument (formerly Textron) lists no designation,[15][16] TS [17] or IPR [18] may be seen.
    • Torx Plus Maxx Stems is a highly specialized variant used on the ends of fastener opposite the bolt-head, and provides higher torque than other drive systems allow.[19] Torxstem is a stud with the Torx Plus Maxx drive on both ends.
  • A modified version of Torx called Torx TTAP was developed in 2005,[20] which features a second recess to create a "stick-fit" engagement, designed to minimize wobbling without the need for magnetic bits, a feature that can be important to certain industrial users.[21] Standard Torx drivers can be used to drive TTAP screws, but TTAP drivers will not fit standard Torx screws.[22]
  • AudiTorx is a tamper-proof fastener where a concave and smooth fastener head is topped with a break-away Torx drive that snaps off when the engineered torque is reached, leaving a rivet-like bolt head that can't be easily removed. The main application for these fasteners is in the railroad industry.[23]

Competitive variants

AW drive is a similar hexalobular type screw head to Torx, with a tapered profile to aid in centering, developed by the Würth Group in Germany.[24] Available in five sizes: AW 10, AW 20, AW 25, AW 30 and AW 40.[25]


Torx-Bits T15-T20-T25-T30

Torx bits T15, T20, T25, and T30

Torx 01 KMJ

A Torx wrench


Closeup of Torx screwdriver tip

18-03-22-Schrauben-M6x20 RRK3361

See also


  1. ^ a b c U.S. Patent 3,584,667, Bernard F Reiland, "Coupling arrangement and tools for same", filed 1967-03-21
  2. ^ 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. In 2014, Acument was sold from Platinum Equity to Fontana Gruppo.
  3. ^ ISO 10664:2005,, retrieved 2012-01-14
  4. ^ Paul Sharke (June 2005). "Fast and Secure: how much proof is tamperproof?". Mechanical Engineering. 127 (6): 32. ISSN 0025-6501. Archived from the original on 2007-02-09. Retrieved 2012-01-14.CS1 maint: BOT: original-url status unknown (link)
  5. ^ "US Patent #2,474,994 Claims, Page 7".
  6. ^ a b c d e "Chart of Torx fasteners and tools". Wiha Tools USA. Archived from the original on 2015-12-26. Retrieved 2012-01-14.
  7. ^ a b "TORX Drive System" (PDF). Textron Fastening Systems. Archived from the original (PDF) on 2007-01-02.
  8. ^ "16pc torx bit set". Amtech Tools. Retrieved 24 February 2017.
  9. ^ "2 Pcs T35 3/13 Torx Head Screwdriver Link 1/2 Square Mechanic Drive Socket".
  10. ^ "FTX47E, Socket Driver, TORX, GM-Style, T47".
  11. ^ "Fiero Torx Sockets".
  12. ^ a b "TORX PLUS Drive System" (PDF). Acument.
  13. ^ "TORX PLUS Long arm L-Keys". Wiha Tools USA. Archived from the original on 7 October 2015. Retrieved 14 July 2016.
  14. ^ Egon Pavlis (16 March 2010). "When a Phillips is not a Phillips Plus So Much More!". Instructables.
  15. ^ "Fastening Solutions" (PDF). Acument.
  16. ^ "Tamper-Resistant TORX PLUS Drive System" (PDF). Textron Fastening Systems. Archived from the original (PDF) on 2006-11-10.
  17. ^ "TS Star Bits (5 Sided) 1/4"D 7pc - Part No. 3389 - Part of the TS Star/Torx* Plus range from Laser Tools". Retrieved 14 July 2016.
  18. ^ "Security TORX PLUS Insert Bits". Wiha Tools USA. Archived from the original on 13 December 2015. Retrieved 14 July 2016.
  19. ^ "TORX PLUS® MAXX Drive System".
  20. ^ US patent 6951158, Jone Edland, "System comprising a screw and a tool therefor", issued 2005-10-04
  21. ^ "TTAP Fastener". Acument Global Technologies. Retrieved 26 February 2017.
  22. ^ "Torx TTAP Advantages". TTAP Drive AS. Retrieved 26 February 2017.
  23. ^ "Acument Industrial fastening systems".
  24. ^ "Technical Information on Fasteners: Design recommendations 11.1 Inside drives for screws – AW drive (AW-Antrieb)" (PDF). Adolf Würth GmbH & Co. KG. Retrieved 2 March 2017.
  25. ^ "Construction Range Overview (Fasteners: Introducing the AW Drive System, p3)" (PDF). Würth New Zealand. 2016.

External links

Bolt (fastener)

A bolt is a form of threaded fastener with an external male thread. Bolts are closely related to screws.

Cam out

Cam out (also cam-out or camming 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. Repeatedly camming out damages the screw, and possibly also the screwdriver, and should normally be avoided.


A chinrest is a shaped piece of wood (or plastic) attached to the body of a violin or a viola to aid in the positioning of the player's jaw or chin on the instrument. The chinrest may be made of ebony, rosewood, boxwood, or plastic. It was invented by Louis Spohr in the early 19th century; historically, this has been explained as a response to increasingly difficult repertoire which demanded freer left hand techniques than had previously been used; however, Spohr intended his small block attached to the bout to protect the tailpiece, which he reportedly broke with his vigorous playing. However, after being promoted by prominent violinists of the day, such as Pierre Baillot and Giovanni Battista Viotti, it gained quick acceptance among most violists & violinists and is today considered a standard part of the viola and violin.

Computer case screws

Computer case screws are the hardware used to secure parts of a PC to the case. Although there are numerous manufacturers of computer cases, they have generally used three thread sizes. The Unified Thread Standard (UTS) originates from the United States, while the ISO metric screw thread is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimetre.

The #6-32 UNC screws are often found on 3.5" hard disk drives and the case's body to secure the covers. The M3 threaded holes are often found on 5.25" optical disc drives, 3.5" floppy drives, and 2.5" drives. Motherboards and other circuit boards often use a #6-32 UNC standoff. #4-40 UNC thumb screws are often found on the ends of DVI, VGA, serial and parallel connectors.

More modern cases from certain manufacturers (Dell, Gateway) and enthusiast cases will lack screws altogether, instead utilizing a tool-less design.

Dell Adamo

Adamo (Latin for "To fall in love with" was a Dell slim luxury ultraportable subnotebook focused on design and mobility intended to compete with Apple's MacBook Air laptop..

A prototype was unveiled at the Consumer Electronics Show on January 9, 2009. In 2008, Dell claimed it to be the "world's thinnest laptop", at 16.5 mm (0.65 inches) thick.The Adamo line was discontinued in 2011.

Hex key

A hex key, Allen wrench or Allen key, is a tool used to drive bolts and screws with hexagonal sockets in their heads.

The Allen name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, and currently owned by Apex Tool Group, LLC. Its genericised use is discouraged by this company. The standard generic name used in catalogues and published books and journals is "hex key".

List of Iron Fist characters

Iron Fist is an American web television series created for Netflix by Scott Buck, based on the Marvel Comics character of the same name. It is set in the Marvel Cinematic Universe (MCU), sharing continuity with the films of the franchise, and is the fourth in a series of shows that will lead up to a Defenders crossover miniseries. The series stars Finn Jones as Danny Rand / Iron Fist, with Jessica Henwick, Tom Pelphrey, Jessica Stroup, and Sacha Dhawan also starring. They are joined by Ramón Rodríguez, Rosario Dawson and David Wenham in the first season, with Simone Missick and Alice Eve starring in the second. In addition to original characters, several other characters based on various Marvel properties also appear throughout the series.

List of screw drives

A screw drive is a system used to turn a screw. At a minimum, it is a set of shaped cavities and protrusions on the screw head that allows torque to be applied to it. Usually, it also involves a mating tool, such as a screwdriver, that is used to turn it. The following heads are categorized based on commonality, with some of the less-common drives being classified as "tamper-resistant".

Most heads come in a range of sizes, typically distinguished by a number, such as "Phillips #00". These sizes do not necessarily describe a particular dimension of the drive shape, but rather are arbitrary designations.

Pentalobe security screw

The pentalobe security screw (Apple nomenclature), or pentalobe screw drive, is a five-pointed tamper-resistant system used by, but not limited to, Apple in their products. Pentalobe screws were adopted by Apple starting in 2009, when they were first implemented in the 15-inch MacBook Pro. They have since been used on other MacBook Pro, MacBook Air and iPhone models. Apple attracted criticism upon the introduction of the pentalobe screw; it was seen by some as an attempt to lock individuals out of their devices. However, inexpensive pentalobe screwdrivers, manufactured by third parties, are relatively easy to obtain.Pentalobe screw sizes include TS1 (0.8 mm, used on every iPhone after and including the iPhone 4), TS4 (1.2 mm, used on the MacBook Air and the MacBook Pro with Retina display), and TS5 (1.5 mm, used on the 2009 MacBook Pro battery). The TS designation is ambiguous as it is also used for the Torq-set screw drive.

Preferred metric sizes

Preferred metric sizes are a set of international standards and de facto standards that are designed to make using the metric system easier and simpler, especially in engineering and construction practices. One of the methods used to arrive at these preferred sizes is the use of preferred numbers and convenient numbers such as the Renard series, the 1-2-5 series to limit the number of different sizes of components needed.

One of the largest benefits of such limits is an ensuing multiplicative or exponential reduction in the number of parts, tools and other items needed to support the installation and maintenance of the items built using these techniques. This occurs because eliminating one diameter fastener will typically allow the elimination of a large number of variations on that diameter (multiple thread pitches, multiple lengths, multiple tip types, multiple head types, multiple drive types, and the tools needed for installing each, including multiple drill bits (one for each different thread pitch, material, and fit combination).


A screw is a type of fastener, in some ways similar to a bolt (see Differentiation between bolt and screw below), typically made of metal, and characterized by a helical ridge, known as a male thread (external thread). Screws are used to fasten materials by digging in and wedging into a material when turned, while the thread cuts grooves in the fastened material that may help pull fastened materials together and prevent pull-out. There are many screws for a variety of materials; those commonly fastened by screws include wood, sheet metal, and plastic.


A screwdriver is a tool, manual or powered, for screwing and unscrewing (inserting and removing) screws. A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear, treated with a dark tip coating for improved visual contrast between tip and screw—or ridged or treated for additional 'grip'. Handles are typically wood, metal, or plastic and usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips that fit into a socket on the end of the shaft and are held in mechanically or magnetically. These often have a hollow handle that contains various types and sizes of tips, and a reversible ratchet action that allows multiple full turns without repositioning the tip or the user's hand.

A screwdriver is classified by its tip, which is shaped to fit the driving surfaces—slots, grooves, recesses, etc.—on the corresponding screw head. Proper use requires that the screwdriver's tip engage the head of a screw of the same size and type designation as the screwdriver tip. Screwdriver tips are available in a wide variety of types and sizes (List of screw drives). The two most common are the simple 'blade'-type for slotted screws, and Phillips, generically called "cross-recess".

A wide variety of power screwdrivers range from a simple 'stick'-type with batteries, a motor, and a tip holder all inline, to powerful "pistol" type VSR (variable-speed reversible) cordless drills that also function as screwdrivers. This is particularly useful as drilling a pilot hole before driving a screw is a common operation. Special combination drill-driver bits and adapters let an operator rapidly alternate between the two. Variations include impact drivers, which provide two types of 'hammering' force for improved performance in certain situations, and "right-angle" drivers for use in tight spaces. Many options and enhancements, such as built-in bubble levels, high/low gear selection, magnetic screw holders, adjustable-torque clutches, keyless chucks, 'gyroscopic' control, etc., are available.

Set screw

A set screw is a type of screw generally used to secure an object within or against another object, normally not using a nut (see bolts compared with screws). The most common examples are securing a pulley or gear to a shaft. Set screws are usually headless (also called blind), meaning that the screw is fully threaded and has no head projecting past the major diameter of the screw thread. If a set screw has a head, the thread will extend all the way to the head (whereas a bolt might have an unthreaded shank between the head and thread). A grub set screw (known in the US as a “blind” screw) is almost always driven with an internal-wrenching drive, such as a hex socket (Allen), star (Torx), square socket (Robertson), or slot. The set screw passes through a threaded hole in the outer object and is tightened against the inner object to prevent it from moving relative to the outer object. It exerts compressional or clamping force through the bottom tip that projects through the hole.

An example application is when a set screw is screwed into a pulley hub so that its end-point bears firmly against the shaft. The fastening action is by friction between the screw and the shaft, often (but not always) with some amount of elastic or plastic deformation of one or both.


Stardrive may refer to:

StarDrive, a 4X space strategy game released in 2013 for Microsoft Windows

"Star drive", alternate name for Torx screw drives

"Stardrive", a 1981 episode of Blake's 7

Star*Drive, a setting for the role-playing game Alternity, published in 1998 by TSR, Inc.

Stardrive, a type of propulsion system found in Stargate

Swirl flap

Swirl flaps are small butterfly valves fitted to the intake manifold just before the cylinder head intake ports of many modern automotive engines, including those from Mazda, Audi, BMW, Vauxhall and Alfa Romeo. The flaps are smaller than the intake runners and therefore allow air to pass around them even when "closed". The photo shows a cleaned swirl flap removed from the intake manifold of a BMW M47TU 2-litre diesel engine. The flap itself is made from stainless steel and secured to a spindle by two small Torx screws. The sealing O-ring and external actuating lever can be seen below the flap itself.


T20 T.20, T 20 or T-20 may refer to:

Twenty20, a twenty over per team form of cricket

T-20 Summit, an international summit for think tanks from the G-20 countries

T20 Medium Tank, a World War II United States tank

T-20 armored tractor Komsomolets, a World War II Soviet Union Artillery tractor

Prussian T 20, a 1922 German ten-coupled 2-10-2 tank steam locomotive

Suzuki T20, a motorcycle

DSC-T20, a digital camera in the Sony Cyber-shot T series

Slingsby T.20, an aircraft made by Slingsby Aviation

T-20, also called Enfuvirtide, an HIV drug.

AT-20, the U.S. Army Air Forces designation for the Avro Anson

T20 (classification), a disability athletics classification for intellectual impairment

T20 size of Torx screw head


T45, T.45 or T-45 may refer to:

T-45 Goshawk, a version of the BAE Hawk modified for carrier-based training

Cooper T45, a Cooper Car Company car

SJ T45, a 1971 a Swedish diesel-electric locomotive

Slingsby T.45 Swallow, a British glider

T45 Roadtrain, a 1988 Leyland Motors tractor truck

T45, Poisoning by primarily systemic and haematological agents, not elsewhere classified ICD-10 code

Type 45 destroyer, an air defence destroyer developed for the Royal Navy

T45, a disabled sports handicap class for arm amputees

T45, a size of Torx screw head


A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.

In Commonwealth English (excluding Canada), spanner is the standard term. The most common shapes are called open-ended spanner and ring spanner. The term wrench is generally used for tools that turn non-fastening devices (e.g. tap wrench and pipe wrench), or may be used for a monkey wrench - an adjustable pipe wrench.In North American English, wrench is the standard term. The most common shapes are called open-end wrench and box-end wrench. In American English, spanner refers to a specialised wrench with a series of pins or tabs around the circumference. (These pins or tabs fit into the holes or notches cut into the object to be turned.) In American commerce, such a wrench may be called a spanner wrench to distinguish it from the British sense of spanner.

Higher quality wrenches are typically made from chromium-vanadium alloy tool steels and are often drop-forged. They are frequently chrome-plated to resist corrosion and for ease of cleaning.

Hinged tools, such as pliers or tongs, are not generally considered wrenches in English, but exceptions are the plumber wrench (pipe wrench in British English) and Mole wrench (sometimes Mole grips in British English).

The word can also be used in slang to describe an unexpected obstacle, for example, "He threw a spanner into our plans" (in U.S. English, "monkey wrench").

ISO standards by standard number

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