The metal "track" that is used to join glass pieces in stained glass windows is called came in the United States and calme in the U.K and Australia.
Came is available in different metals. Lead (solid), zinc, copper and brass (all hollow) are most popular with lead being the most common.
There are also a variety of shapes (specified by the end view -- see link to illustration below). I-beam is used for the window interior where two pieces of glass meet. U-shaped is typically used to "frame" a project.
Came also comes in a wide variety of sizes to accommodate different thicknesses of glass and to allow different design lead-line widths. Additionally, the surface of the came that is visible, once a window is assembled, can be either flat or curved.