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How do H-shaped lead strips hold stained-glass pieces together?

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The north rose window at Chartres Cathedral in France, featuring intricate stained glass with vibrant geometric and biblical designs in a large circular and five tall vertical panels. — stained glass The stained-glass rose window in the north transept of Chartres Cathedral, France.

In the traditional art of stained glass, H-shaped lead strips—often referred to as "leads"—serve as the structural framework that holds individual pieces of glass together.

The process functions as follows:

Design and Cutting: After glass pieces are cut and shaped to fit a specific design, the glazier accounts for the width of the lead strips that will separate them.1
Assembly: The glazier places the glass pieces into the grooves of the H-shaped lead strips. By butting the strips against the edges of the glass, the lead acts as a channel that secures each piece in place.1
Securing the Panel: Once the pieces are arranged across the glazing bench, the joints where the lead strips meet are soldered together to create a cohesive unit.1
Finishing: To ensure the panel is stable and weather-resistant, a putty compound is rubbed under the leads to waterproof the assembly.1

Because lead is flexible, larger windows require additional support from iron armatures or stone mullions to maintain their structural integrity.1