The lead framework holding pieces of stained glass together is called cames.
A came is a strip or channel, traditionally made of lead, that surrounds the edge of a glass piece. Glaziers fit cut pieces into the channels and join the intersections with solder, producing the flexible network characteristic of traditional stained-glass windows.
Cames do more than outline the design: they also help support the glass panel. Large panels may need additional reinforcing bars because lead is relatively soft and can gradually deform under its own weight. Protective glazing and careful maintenance can reduce weather-related damage.
Cames are often confused with tracery. Tracery is the stone framework of a Gothic window opening, while cames are the smaller metal strips inside a glazed panel. Mullions are vertical or structural divisions, usually made of stone, wood, or metal.