What is Torx?

Torx is a screw drive with a six-pointed, star-shaped recess in the head of a screw or bolt. The system was developed in the late 1960s by the American company Camcar Textron. Torx is a brand name; the generic, standardised name is the hexalobular drive, defined in ISO 10664.

How it works

The six rounded lobes of the bit engage the walls of the recess almost at right angles. This transfers force better than a cross-head (Phillips or Pozidriv) drive:

• Less cam-out: the bit is not pushed out of the recess, so you need less pressure while driving.
• Higher torque without stripping the head.
• Less wear on bit and screw head, and the screw stays on the bit more easily.

Sizes

Torx sizes are written as a T followed by a number, such as T10, T20, T25, T30 and T40. The higher the number, the larger the profile. Thicker wood screws use larger T sizes; the exact size for a screw is printed on the box.

Variants

• Tamper-resistant Torx: with a small pin in the centre, so a standard bit will not fit. Used against vandalism.
• Torx Plus: a further developed profile with even better torque transfer, marked IP.
• External Torx (E sizes): the star shape is on the outside of the head, like a hex head, and is driven with a Torx socket.

Practical tips

• Always use exactly the right size. A T20 in a T25 head will just about grip, but it damages the recess.
• Replace worn bits in time: a rounded bit ruins the head.
• Use impact-rated bits in an impact driver.
• A Torx bit is not a hex (Allen) key. They sometimes half fit, but damage both.

Related terms

• Allen key
• Countersink bit
• Spirit level

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