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

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 numeral "6", not a capital "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.

Principles of operation

The angle between the plane of contact between tool and fastener and the circumferentially directed force is much closer to 90 degrees 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] Where Phillips heads were designed to cause the driver to cam out[citation needed], to prevent overtightening, 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 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 manufacturer claims that this combination can increase tool bit life by ten times or more.[citation needed]

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 on the right 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 diagram does not show a true Torx profile, but illustrates the general shape and geometry.

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. It can be seen that for the Torx type of design, the angle is much closer to 90 degrees 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.


Part of a series on
Screw drive types
Screw Head - Slotted.svg Slot
Screw Head - Phillips.svg Phillips
Screw Head - Pozidrive.svg Pozidriv (SupaDriv)
Screw Head - Square External.svg Square
Screw Head - Robertson.svg Robertson
Screw Head - Hex External.svg Hex
Screw Head - 12-Point External.png
12-point flange
Screw Head - Hex Socket.svg Hex socket (Allen)
Pin-in-hex socket screw drive 003.png Security hex socket (pin-in-hex-socket)
Screw Head - Torx.svg Torx
T & TX
Screw Head - Torx Tamperproof.svg Security Torx
Screw Head - Tri-wing.svg Tri-Wing
Screw Head - Torq-set.svg Torq-set
Screw Head - Spanner.svg Spanner head
Screw Head - Clutch Type G.svg Clutch
A & G
Screw Head - One-way Clutch.svg One-way
Double-square screw drive 001.png Double-square
Screw Head - Triple Square.svg Triple square
Screw Head - Polydrive.svg Polydrive
Screw Head - Spline.svg Spline drive
Screw Head - Double Hex.svg Double hex
Screw Head - Bristol.svg Bristol
Pentalobular.svg Pentalobe

Torx head sizes are described using the capital letter "T" followed by a number ranging from T1 to T100.[5] 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.[6] The "E" numbers are different from the "T" numbers of the same size: for example, an E4 Torx socket fits a T20 head.[5]

Properties of various Torx drives[5]
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
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[13][14] 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


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 E40, while E8 Torx socket will fit a T40 Torx bit [5]).
Properties of various External Torx drives
Size   Point-to-point distance [15]    Standard fastener selection [6] 
(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 [16] (sometimes listed as IP1 to IP100 [17]) 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.[16] 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.[18] Though Acument (formerly Textron) lists no designation,[19][20] TS [21] or IPR [22] may be seen.

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.

AW is a similar type of screw head developed by the Würth group in Germany.


See also


  1. 1.0 1.1 1.2 U.S. Patent 3,584,667 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<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. Fast and Secure,, retrieved 2012-01-14<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. 5.0 5.1 5.2 5.3 Chart of Torx fasteners and tools,, retrieved 2012-01-14<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. 6.0 6.1
  8. "SMALL TORX TRX STAR SCREWDRIVER BITS T5 T5 5 T6 T7 T8 T9 ON 1 2 HEX SHANK".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  9. "Am-Tech Tools 16pc Torx and Tamperproof Bit Set".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  11. "Bitsatz "LongPro" 32-teilig (CHL17885) bei Trenkenchu & Stadler GbR".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  12. "2 Pcs T35 3/13 Torx Head Screwdriver Link 1/2 Square Mechanic Drive Socket".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  13. "FTX47E, Socket Driver, TORX, GM-Style, T47".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  14. "Fiero Torx Sockets".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  16. 16.0 16.1
  18. "When a Phillips is not a Phillips Plus So Much More!". 16 March 2010.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links

  • Media related to Torx at Wikimedia Commons