Helmet M40

[Papi]

Hi, today I got some German helmets. While cleaning, I noticed an unknown marking. I heard that according to the markings you can trace the component for which the helmet was made. Marked on the back only: Q66 nN507.
If anyone has info, please contact me. Thank you very much.. (Sorry for my english)

[MAP]

This is a rear marked later war Quist made helmet

Q stands for Quist
66 stands for the size of the shell

And below that the DN 507 is the batch/lot # of the steel that was used to make the helmet.

To add, and I'm sure you know this. All the helmets shown have been repainted (probably recently) and the liner in the photo is not German.

[Papi]

Yes, in my country it was used by firefighters after the war..

[Schwerpunkt]

I heard that according to the markings you can trace the component for which the helmet was made.
If anyone has info, please contact me. Thank you very much.. (Sorry for my english)

That is false information , the number is just a steel lot number , hundreds of helmets will have the same number and will have received different decals.
What we can say is that Dn507 would not have received a decal.