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Torx Bit Styles & Sizing

Susan Revermann

A Torx screw or bolt contains a 6-pointed star pattern on the head. It was developed by Camcar Textron. This is a trademark name and star, star screwdriver or star bits can be used to refer to the same item. These screws and bolt need special tools for installing or removing and they offer extra security while resisting stripping or overtightening of the screw or bolt head. You will find these on all sort of applications, including vehicles, tools, computers and electronics.

Standard Torx

Special tools are required for Torx screws and bolts.

A standard Torx has a round external head with an internal six-pointed star in the middle. A Torx tool is needed to insert into the head to turn these screws. Torx head sizes are designated with a “T” with a number after it. The size range for these is from T1 to T100 and they indicate a measurement from one point of the six-pointed star to the adjacent point. The smaller the number, the smaller the dimensions of the screw head. T1 has a .031 inch diameter point to point or a .81 mm diameter point to point. The max torque for a T1 is .02 to .03 Nm, where Nm equals 8.851 lbf in. T100 runs at .871 inches point to point or 22.13 mm point to point. These have a max torque at 1843 to 2048 Nm.

External Torx

External Torx heads have an external-six pointed star head. An external Torx driver is also called a security Torx, tamper resistant Torx or pin-in-Torx. These torx drivers cannot be turned with a regular Torx driver or flat-head screwdriver. A special Torx socket must be used to turn it. The sockets for these kinds of bolts are designated with an “E” followed by a number that indicates a point to point measurement. These range from E-4 to E-24. E-4 is .15 inch point to point or 3.8 mm point to point. E-24 is .87 inch point to point or 22.1 mm point to point.

Tamper-Resistant Torx

There is a tamper-resistant Torx that only has five points instead of the usual six. You will find a solid post in the center of these. A special torx driver must be used to turn these and these can prove difficult to find. These Torx are called Torx TS and are considered a security screw or bolt. The sizes for these follow the regular sizing for standard Torx.

Torx Plus

When the original patent for the first Torx ran out in 1990, a new Torx version became available. These are called Torx Variant or Torx Plus. The design for these helped improve the torque capacity while lowering the incidences of wear or stripping of the Torx head. You can use a regular Torx tool for these but you won’t be able to tighten it as much as it needs. A special tool is required if you want a tight fit. The driver sizing for Torx Plus is designated with a number followed by an “IP.” These range from 1IP to 100IP. You will find pan head Torx, flat-head Torx and socket head Torx Plus. The pan and socket heads are the same measurements, with the flat-head only slightly bigger. 1IP for a for pan and socket heads is M.09 and the flat head Torx is M.9 and M1. The 100IP only has a 7/8-inch and 1 inch socket head and an M22 and M24 metric socket head. The “M” designates metric measurements.


To remove Torx screws and bolts, you have a few options. There are Torx sockets you use with your regular socket wrench. You match up the Torx screw or bolt size with the socket. These are used with external Torx. There are also Torx screwdrivers that have the six-sided star on the end. These are used with the standard internal Torx heads. Torx Plus screws and bolts have their own Torx Plus driver, called Torx TS, to be used for the best tightening. Specialty Torx screws and bolts need to have specific tools to be used just for them. You can find any of these tools online or from the Torx distributer from which you bought the Torx screw or bolt.