Unidentified copper lid for...?

[timefuze]

Hi colleagues,

I found 3 copper lids almost on top of each other under the ground. They've no markings on them. In the inside of the lid remnants of a circular felt sealing are attached by a central, rivetted clamping. Looking at the construction, I'd think the "lid" fitted on a tubular object with an outside diameter of approx 45mm and inside diameter of 25mm minimum.
I've no clue what this lid is. Can someone enlighten me on this please? See pictures.

Many thanks in advance.

Timefuze

 

[millsbomber]

Iv Seen these before in Europe but for the life of me i cannot remember where, i think there was some sort of packing material inside the lid that made a soft fit when screwed down, how did you come by it,,,,,,, Dave

 

[APFSDST]

This is transport cap for Dutch 81mm mortar grenade.

 

[timefuze]

Hi APFSDST & millsbomber,

Thanks a lot for the hint. In the area that I found these lids, Germans shot with 81mm mortars, using German, French and -apparantly- also Dutch ammo.
How does this cap fit onto the mortar grenade, please? The outside diameter is only 45mm. Was it used to protect the top or bottom?

Txs.,

Timefuze