M1 - odd heat stamp number

[Kromal]

Thank you for your replies.

the famous dimple over the loop

Could you explain this sentence?

I found this topic Some pics of my mint M1 Schlueter shell

and I think my M1 is really similar to those helmets.

[earlymb]

You can see a dimple in the inside edge, maybe used for positioning the chinstrap bales. I think that's what rudder means?

The helmet in that topic is mine, it's an untouched, mint original Schleuter and an excellent guide for the correct colour and texture. I think your helmets are fine and possibly re-issued for Korea and/or Vietnam, although they seem to have their original WW2 paint.