A part dropped off my bike and I`m not too sure of it`s purpose-a guard of some sort?

[night cycler]

About a month ago during a cleaning session, this plastic guard fell off of the steel chain guide (Note: chain guide is probably not the correct name-but I don`t know any better-see photo). I tried to replace it with my oversized oily fingers without any element of success. I gave up in the end. I also observed that the small plastic hooks to hold it in place (that are part of the plastic on the reverse side) appear to be misshaped or distorted.

I`m not unduly concerned but I`m saying this without knowing for sure what it`s purpose is. If it is a guard, I imagine it stops the chain rubbing on the guide, but there are no rubbing marks

 

[lpretro1]

Photo a bit blurry but that looks like the plastic insert that fits into the 11spd front mechs - it is there to assist in smoothing the gear change. They are intended to wear out and are replaceable - they cost about £1.99 and you should replace it - then check gears - in small front ring/biggest rear cog then there should be a mere smidgen of a gap - 0.5mm. Without it the gear change may be a little raggy.