If you search for Stahlhelm on this forum you will find plenty of pictures of original examples to compare with, but typically the rim looks much more professionally rolled, the protrusions have the wrong proportions, and the leather band inside the helmet should be a single thick piece of leather instead of being sown together; in addition the leather looks artificially aged.
This is how it should look when it's original.
Compare the differences, and you'll know. It is a completely original GBN64 marked M16, which I had in my former collection.
Gebruder Bing, Nurnberg, size 64.
This is a Chinese production.Leather painted with wood stain.The strap is not worn out from the inside.The Chinese in another version soak the helmet in pig manure for three months.You have to know the enemy to fight him.