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Looks like a little plastic split wedge to keep the upper bearing in place. I need a replacement for it because I've chipped it trying to remove my forks!
You've answered your own question. 8)
I've tried searching for that on CRC and I'm turning nothing up though 🙁
[s]It's... a split wedge. Or split cone, or centring cone, or expanding-thingywotsit-from-a-headset, doesn't really matter what it's called as I doubt you'll be able to get an exact fitting one to replace it on its own anyway. How bad is the damage? It doesn't matter if it's a bit chipped, so long as you can tighten out any play in the headset it'll do it's job just fine.[/s]
Edit: no, wait, assuming that's your exact headset up there, Acros call it a 'plastic compression ring'. And apparently you can get a new one from them [url= http://www.acros.de/SERVICE/FAQ/STEUERSAeTZE:::6_75_169.html?language=en ]for the price of a couple of Euro stamps[/url].
I'd call that a compression ring
its the compression ring
[url= http://www.evanscycles.com/products/m-part/elite-headset-spare-expansion-compression-ring-1-1-8-inch-ec039874 ]link[/url]
Cheers, I've asked them for an address or a method to pay for the postage. Might as well replace the lower bearing in the meantime.
Thanks to everyone else too.