Screw Head Types
Modern screws employ a wide variety of designs to drive or extract them, each requiring a different kind of tool. Some types of drive are also only intended for use with automatic technology, for instance, on production or assembly lines. The most common screw drives are detailed below.
Slotted (or Flat Head)
Slotted screwdrivers are available with either flared or parallel tips. For the majority of uses, a flared tip is ideal but if the screw needs to be driven below the substrate’s surface, a parallel tip screwdriver should be used. With slotted screwdrivers it is always important to ensure that the driver’s tip matches the width of the screw slot, otherwise you risk damaging the screw head.
The Phillips® screw has four simple, tapered slots and is designed for use with a Phillips® tip screwdriver, which delivers increased levels of torque. Should the torque levels become excessive for the tip however, it will wind itself out of the screw. This prevents over-tightening and the risk of damage to the screw head..
A Hex socket screw has a hexagonal recess in the head and is driven by a hex wrench..
Pozi® screws may look similar in appearance to classic Phillips cross-heads but they are actually very different. Pozi® provides four additional points of contact and does not have the same rounded corners as a Phillips® screw drive. This enables is to offer reduced cam out and even higher levels of torque when used with the right tool in good condition. Pozi® screws can be easily distinguished by a line embossed in the screw head at 45° to the slots for the driver.
Torx® (or star bits)
Thanks to their design, Torx® head screws resist cam out much better than Phillips® or slotted screws. Where Phillips® heads have been designed to cause the driver to cam out to prevent over-tightening, Torx® heads have been designed to prevent this and to acheive a desired torque level consistently. Torx® head sizes are denoted using a capital letter ‘T’ followed by a number. A smaller point-to-point dimension of a screw head. Only the proper driver can drive a specific head size without the risk of ruining the driver or the screw.