Engine mounts

[mememe]

I was replacing my starter motor today and I noticed that the passenger side engine mount had something hanging off the bottom of it which the drivers side didn't(it's the rusty looking round thing). Should I have one of these on the drivers side aswell? What is it please?

Also, the passenger side mount doesn't have a rubber boot around it like the drivers side. What are the implications of this.

Drivers side



Passenger side

 

[mememe]

Also. The drivers side mount securing nut was almost falling off the stud (completely undone). This was the cause of my knocking sound when accelerating hard.