There was a big theory in the 1970s that brass hardware - together with really heavy woods - was the secret to great tone and infinite sustain. So you got all these "furniture" looking guitars and basses - like Alembics, for example - made of things like ash and walnut, with big chunky brass bridges and brass nuts. That's why Yamaha SG2000s have under-bridge brass "sustain blocks", and old Ibanez Artists weigh a ton.
Then after a few years people started figuring out a lot of these guitars actually sounded a bit dead and weren't resonant at all. So they started using different materials.
I suspect people of [cough] a certain age [/cough], like me and Feline and Kilby, remember those days very well.
