Beautiful M40 SD! Would have loved to have known the maker, but I guess that's lost to time. Where was this found? Reminds me a lot of the Russian front helmets.
The steel liner ring only denotes who made the liner, not the helmet. Usually, save one or two, the inside of the helmet on the back near the rim has the manufacturer.
This is the inside of my non-relic helmet. The marking is barely visible in the photo for some reason, but it was made by cKL, aka Eisenhüttenwerke - Thale.
Cool, reminds us that the past isn't so long ago. All these WWII relics are still out there, still in comparatively good condition waiting to be found. They are not dust yet, but in the next 100 years or so many will be dust. It's good we find and preserve them as physical reminders that these events were real.