The shank button is a button in which the button sits on top of a metal shank.  This is a button that needs to be sewn on by hand and they come in many different sizes and shapes. They can be used on a variety of different kind of projects, from the delicate with thread loops, to more heavy duty like a coat. Shank buttons are a great addition to decorating your project. You just want to make sure you sew them on right so they stay secure and don't pop off.