Right so today I was having a snoop around the engine bay just in general and I seen this thing what the hell is it?
It's like what you would screw into a hot water bottle. Here is a pic of it

It was just resting next to a hole which was left open, it must've been like this since atleast last May when the car last went to a mechanic, so maybe it was opened for a reason and then they forgot to put it back in. But somehow the thing has just sat there and not fell out even though the car has been used on the motorway and all sorts.
The hole i'm referring to is on the right of the engine down towards the bottom, so in between the engine and the battery it's down below in that gap.
The hole is on what looks like the gearbox I think lol seriously I aint got a clue about stuff like this so please bare with me.
Here is the best pics I could take of the actual hole that was left open, i've since put the plug back into the hole where I assume it goes and the car doesn't judder on idle now but that could just be coinsidence as the car was already warm.
Here are a few pics of the hole lol



Any help and advice is much appreciated.
CHeers
Asif