The parts of hexagon and Torx keys are the same, it is only the shape at the end of the key which differs. Both the long and short arm of an L-shaped hex or Torx key can be used to turn the fastener – which end you choose to use is likely to depend on how much torque you need to apply and the access space around the fastener. Certain parts or features of hexagon and Torx keys may not be found on all types. For instance, the storage handle is only found on folding key sets.
The long arm is the longer of the two sides of an L-shaped hex or Torx key. T-handle keys also feature a long arm. It is used to reach further into recesses on a workpiece or between obstructions to access a fastener.
The short arm is the shorter of the two sides of an L-shaped hex or Torx key. Some T-handle keys will also have a short arm that protrudes only slightly from the T-handle. The keys of folding hex and Torx key sets are also short arms. Short arms are used when space and access around a fastener is not an issue. This allows the long arm to be used as a handle, increasing the torque you can apply to turn the fastener.
Not all hex and Torx keys have ball ends: they will most commonly be seen on standard keys (see What are the different types of hexagon and Torx key sets?), although less expensive sets often don’t have them. The ball end is a rounded end to the shaft instead of the simpler straight cut finish. The ball end is most commonly seen on the end of the long arm, although it can be found on the short arm of some.
The ball end allows the hex or Torx key to be positioned in the head of the fastener at an angle and still be capable of turning the fastener. This feature can help you gain access to hard-to-reach fasteners. For more information about ball ends see What additional features can hexagon and Torx keys have?
T-handle hex and Torx keys provide a more comfortable grip and, in some cases, may enable you to apply more torque, particularly when using the long arm to turn a fastener.
Folding keys are only found on folding hex and Torx key sets. All the keys on folding sets are short arms that fold into a storage case that doubles as a turning handle. The closer to 90 degrees that the key is folded out to, the more torque you can apply, while folding it out closer to 180 degrees will allow you to turn the fastener quicker. For more information see What additional features can hexagon and Torx keys have? and What are the different types of hexagon and Torx key sets?
The storage case/handle is fitted to folding key sets. When a hex key is folded out, the storage case can be used as a handle, to give greater leverage and torque when turning a fastener. When the keys are folded in the handle becomes a storage case for the keys.