Hi Mick,
As James said, very nice helmet for your first. :thumbleft: Most of us started off with a beater.
We did have a discussion some time ago, that pointed to the "f' having a "probable" meaning of Feldbrauchbar which means Field wearable (or field-serviceable). So yes, probably. But I have usually seen these stamps by themselves, not combined with a number like your 171? Tony