What is the primary function of a mandrel in jewelry making?

The primary function of a mandrel in jewelry making is to size a ring. A mandrel is typically a tapered tool that jewelers use to shape and measure rings, allowing for accurate sizing and forming of the metal into the desired circular shape. As jewelers wrap the metal around the mandrel, they can also tap or manipulate the material to create a perfect fit for the wearer. This process ensures that the ring maintains its intended design while achieving the correct diameter.

The other functions mentioned do not align with the use of a mandrel. A mandrel is not primarily designed for cutting metal into patterns, joining two pieces of metal, or fusing glass to metal, which are tasks typically handled by other tools and techniques specific to those processes.