Sorry, don’t know its proper name. What’s it for though? I see self-builds without it, but you seem to get one included when you buy a bike off the shelf. Mine just seems to gather dirt…

Spoke protector. If the rear mech isn’t set properly or gets bent, it can overshift on the cassette and drop the chain into the spokes. A chain under high load will make a mess of spokes. If you want to remove it, you’ll either need to remove the cassette or hack it off around it.

Its to stop the chain going into the spokes.If you have a properly adjusted rear mech you dont need it.Though I`ve lost the chain into the spokes on a couple of occasions and regretted my haste in removing it………….

Dork disk is the derogatory term. It stops the chain damaging the spokes should it come off.

I wish these things were on sale. Once I clipped a mech on a downhill run and snapped 10 spokes and gouged a big lump out of my hub. I dont know why people take them off

Why not go the whole hog?

I wish these things were on sale.

Err, they are

All becomes clear. Thank you.

I thought they were called pie plates, and the sight of one on a fixed-gear bicycle portends the coming apocalypse?

http://bikesnobnyc.blogspot.co.uk/2008/04/pie-in-sky-world-without-spoke.html