Answers on a postcard please...

[JayDub]

I found this on the ground at the rear of the bike today, its quite familiar but i can't think where I've seen it before.  Its rubber a plug/grommet, I was working on the rear light unit a couple of days ago but it may be from a passing car even 
Go on - wheres it from (The bulb is for size comparison).

[GavD]

It's from Wales

[JayDub]

Thanks Gav! 

I just swore at you 

[GavD]

Always happy to help

[Sparky]

That looks like the rubber plug from the clock to seal where the clock bulb goes in.

I just changed my clock bulb to a green LED so I just had all this apart.

[JayDub]

I did think the same as I  was trying to replace the clock bulb yesterday, but thought it was too big for that.
- So, it looks like Sparky wins
and the prize is...................... SATISFACTION! 

Thanks mate! 

[ssevy]

 That's an adapter so you can disprove  the impossibility of trying to fit a square peg into a round hole.

[JayDub]

Thanks ssevvy... you can go stand in the same corner as Gav