What's this, then?

[Gelandestrasse]

Probably been asked before, but what's the extra bit of plastic for that's screwed to the box next to the lock, please?

 

[Wreford Miles]

Air pressure matching thingy me bob, or M16 are tracking you. I can’t remember which

 

[Khulu]

Air pressure matching thingy me bob, or M16 are tracking you. I can’t remember which

You're not helping!

 

[wrinkleyowlie]

When left open it allows the box to stabilise at the same atmospheric pressure as the air around it. Early boxes where known to distort at varying altitudes.

 

[gazza12adv]

I had a few occasions when opening a box at the top of a mountain, get back down to a campsite or whatever and there was a significant vacuum inside the box, so much so that it was almost impossible to open it, this is an airvent, this was back when the seals used to work well though.

 

[Daffy]

And be impossible to open in some circumstances due to a lower pressure inside the box creating a lid that could not be opened. DAMHIK

 

[SteveM]

I think you'll find that this device cunningly doubles up as a handy in-built helmet scratcher which you'll find on the corresponding area on the inside of the box.

 

[Gelandestrasse]

Many thanks all; this is a great site.