Headset spacers.

All much of a muchness TBH. Unless you want extra blingy ones.

Yep, plus the job they do is incredibly simple. Like, people worry about "taking a perfectly good carbon tube and cutting it up", which is how pretty much all carbon spacers are made but it's just a nonissue with the stresses involved. Especially as they're usually pretty fat.

I 3d printer some, on a cheap machine and out of really shitty plastic to boot, just a terrible idea but they worked absolutely fine, for a while anyway! I don't recommend it but it gives an idea of how crappy a spacer can be and still work.