Iron fist training is similar to iron palm except the focus is only on the fist (during a punch) as opposed to the palm, or the entire hand. With iron fist training, the training bag can be placed on a vertical surface such as a wall or tree and punched, or less commonly placed on a table and struck with downward blows similar to how it is done with the palm.
Much like with palm conditioning, in iron fist training the bag is first filled with rice or mung beans and over time they are replaced with harder materials such as gravel and steel shot. The student stands in front of the hanging bag and takes the appropriate stance and then delivers a series of punches into the bag, ensuring good penetration. Sometimes after a certain number of punches the student will stop and shake out or massage his hands to help promote blood flow and healing.
As with any type of body conditioning, progress must be made slowly as trying to do too much too fast can result in injury to the practitioner. Iron fist training may use standard dit da jow, or it may have its own variety of liniment. Some schools use regular dit da jow to help keep the hands appearing healthy. Other schools have special liniment that helps promote callous creation on the knuckles which can help make the hands tougher, but also results in unsightly callouses.
Each kung fu school will have its own regimen for how many punches to throw ,how to throw them, and what stances to use. When trained correctly, iron fist training can result in the ability to deliver a very powerful punch.