The tuning pin foot is of particular interest to piano tuners. Understanding when it moves, when it doesn't move, how to get it to move, and when we need to worry about setting it so it doesn't move anymore, called "Setting the Pin" (we do NOT need to set the pin every time we tune a piano) is critical if we want to understand what needs to happen in order to produce a stable string.
This short course introduces you to the Pin Foot and how it behaves when we try to turn the pin.
Are you looking for some more theory?
This book has you covered!