Torx is a type of screw head manufactured with a star-shaped end. A Torx bit is used to insert and remove Torx-head screws. Because screws do not come with the head size written on them, users must determine what size the screw is in order to select the right-size Torx bit for the job. To save time and the headache of trying all the sizes of Torx bits you have, you can measure the Torx-head screw.
Measure the Torx-head screw with a tape measure or ruler. Start at the top of the screw and measure from one star point across to the star point farthest away.
Move your ruler or tape measure to the circle within the star points of the tip of the Torx-head screw. Measure the width of just the circle.
Compare your measurements with one of the online charts at Home Metal Shop Club or Wiha Tools (see Resources) to see what size Torx bit must be used for the Torx-head screw you have.