Some fixtures hang their shade on a stem. The beaded-chain fixture hangs it on chain, and that choice makes the whole thing lighter than a rigid fixture. It's a specific look, and it depends on small parts that are easy to lose and specific to replace.
The chain is the fixture
The design suspends a glass shade, or sometimes a bowl, from three or more lengths of fine beaded metal chain, hanging from a canopy at the ceiling. Instead of a solid stem, you get delicate chains and open air, so the shade seems to float below the ceiling. It was a popular way to hang a diffusing bowl or shade in the early-to-mid twentieth century, and it suits rooms that want a soft, suspended light without a heavy fixture.
The beaded chain itself is the defining part and the vulnerable one. It's finer and more decorative than the sturdy chain used for weight-bearing pendants, chosen for looks as much as strength, and over decades a link fails, a chain goes missing, or the finish wears. The connectors matter too: the small loops, holders, and canopy fittings that join the chain to the shade and the ceiling are specific to this kind of fixture, and a missing one strands the whole assembly.
Salvager's Note: A beaded-chain fixture with one chain gone isn't fixable with generic chain; the replacement has to match the others in size, style, and finish, or the fixture reads as patched. When you buy one, confirm all the chains and the canopy fittings are present.