How does the petrol cap fit together, please?

[nomis 12]

My petrol cap somehow managed to ping out of the car and end up on the floor in pieces.

(Don't ask how, the car was at my mum's house on her drive, and I have no idea).

 

The inner bit that goes down the fuel nozzle remained in the car and the outer white plate with the lock attached to the trim ended up on the floor.

 

I can't put it back together again though.

 

There doesn't seem to be anyway to get the two bits to attach to each other - and the spring just pushes them apart.

 

So I have inner bit, outer plate with trim attached and lock and spring.

 

Am I missing a bit?

 

Thanks

 

Simon

 

PS. I have ordered a new standard Valeo locking cap from Euro Car Parts, as I need to get it MOTed.

Am running a temporary cap at the moment from Halfords, which fits tight.