Rear Cog Protective Plate

[brb408wpb]

In cleaning my rather old bike yesterday, I noticed the plastic plate (does it have a name?) was brittle and cracking. To replace it, I believe I need to remove the cogs, pop off the old, and pop on the new. Has anyone done this? Are they one size fits all for your rim size?
Thanks<br />
Bruce

[cyclerUK]

The disc is there to stop the rear derailleur going into the spokes and damaging them.<br />
You actually don't need to have one unless there is a danger of the derailleur overshifting.<br />
There is usually a stop screw, on the derailleur, to counteract this.<br />
If you look at current bikes they don't have the disc.<br />
I would expect all discs to be standard and possibly you could make your own out of suitable plastic.

[brb408wpb]

Thanks. I was at the bike shop today and got a similar answer. They say some people actually break them off and never use them.