Did you know that when prongs for jewelry settings are made, they start off tall and pointy? Before a stone is placed into a setting, the prongs (metal posts) for the setting are much higher. This allows for different size stones to be placed, as well as for shaping to occur. Once the stone is seated, the prongs are filed flush just above the top of the stone. Lastly, a special tool is used to round them over.
The tool is pictured below and has a cup shape to it. This tool comes directly down on top of the metal and gives the rounded feature to the prong.