Within the practice of Taiji Qin Na there are many variations of joint locking techniques that are used ranging from arm & shoulder, wrist and head locks and properly the most quick and effective are finger locks (Zhi Suo).
Finger locks can be easily used by young children and females to help defend themselves, breaking free of grips and holds, as it takes little amount of strength to bend or twist a finger back than an arm or hand.
Finger locks can be used singularly, double or split fingers to either mis-place the bone (Cao gu), or to divide the tendons (fen Jin). In the practice of Taijiquan finger lock Qin Na can be used as a defensive method from grips, holds or from someone pushing and striking at you with an open hand. They can also be used offensively by quickly seizing your attackers fingers to subdue or immobilise them, you can also set your attack up for a finger lock by striking at him or her and then grasp the fingers of his or her blocking arm and bend & twist them.
You must understand that there is no perfect technique for all situations. What you do to defend yourself depends on what your attacker does. And since your attacker is not just going to stand there and let you apply a joint lock on them, you must learn how to adapt your Qin Na to the circumstances. Your Qin Na must respond to and follow the situation, the techniques must be skilful, alive, fast and powerful and your Qin Na must take your attacker by surprise.
It takes a lot of skill to apply any Taiji grabbing Qin Na technique on your attackers body and if he or she is aware of your intention then it makes it extremely difficult to be successful. In that case you will properly need to apply a strike aimed at an energy point (Dian mai) to cause pain or as a distraction.