What is this I found in my sump?

Hi All

I've just had my sump off and when I gave it a clean I found this.
Attachment 83432
Anyone got any ideas what it may be?
I'm leaning towards part of an old oil filler cap.
It is about the right diameter as the existing cap with what appears to be a flat on one face.
The other face is where it was broken off with what could be the start of a thread.

Cheers Shane

What is it made of - metal, plastic, magnetic or aluminium? Bit of an unwanted surprise that one!

Looks like part of oil cap to me,i had a bit break off too,looks just like that.

The bits are hard black plastic- possibly black Bakelite.

Part of the filler cap. Have seen it quite a few times.