Yes Master Pan toughens up one (1) fist, his right by punching steel. Like my friend said, it's scary just looking at it or having tea with him, like he's got some steel welded to his knuckles.
His student taught me the technique, which is more or less just do it, repetitively, just lightly and don't go crazy, let the skin heal sometimes, go again. Even my friend gave me a present... a heavy piece of steel with a flat surface. :) :)

However, i decided agaist it: the impracticalities of lugging around a piece of steel with me. However i sometimes give trees a heavy workout, palms, knuckles and all.
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Which brings up something interesting, Master Pan doesn't use the traditional fist ( like in Karate and most kungfu). If you can get a photo, study where the callouses have developed. You can see there is none on the top first knuckle, but there is one on the third knuckle. Mater Pan does not bend his hand to make flat first two knuckles and back of hand is not parallel in a line with the arm. He uses the "natural fist" with different impact knuckles. It is quite unusual.

To understand what i mean, oberve which knuckles make full contact when you hold your fist against a flat surface. And then how you can change that.
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Well he doesn't have to reach in his pocket for the brass knuckles! :D :D

"It hurts to set you free
But you'll never follow me"