KM gas mask with side screw cap ?

[ITALIANWARFRONT]

the mask is stamped with the classic eagle M.
Both mask and can are named to the same soldier, I was curios to know what is the side cap opening

Giorgio

[ITALIANWARFRONT]

1

[ITALIANWARFRONT]

2

[Lenny W]

Extra lenses

[GAMS1]

To connect a microphone as i remember ?
Nick

[duska]

The side cap is for a telephone attachment.

[Dimitri D]

Here is a picture for illustration of his exact use.

Collection km-spain (hope you are ok Eduardo for posting your picture here).

[ITALIANWARFRONT]

thank you all