Where has this come from?

[parrots mum]

Hoovering the cab mat on the passenger side I spotted a plastic screw/rawl plug which was resting on the fitted cab carpet, next to the cab mat, below the passenger seat. It may have come from under the seat although I couldn't see any empty holes. Any ideas as to where this belongs??
Thanks.

 

[Meoncoast]

picture may help

 

[parrots mum]

I've tried downloading a picture but keep getting the message 'File too big, max allowed size is 2MiB'.Aaargh!!
Never mind--I will have another look and see if I can spot an empty hole.
Di