Volks gas mask packing box question

[camo master]

The lid of the paper packing boxes of Volks gas masks is embossed with the following:

VM
M
or F or K

What do the M, F and K stand for? Do they indicate the size of the mask?

Thanks
Mark

[Gran Sasso]

M = Mann (man)
F = Frau (woman)
K = Kind (child)

So it refers to its size

[camo master]

Excellent
thanks for your quick response
Much appreciated
Mark