P38 magazine:

Mauser P38v U 

Mauser P.38v U magazine P38

In September 1944, Walther discontinued the hardening process of the magazine feed lips. The Mauser magazines produced without the hardening process probably were put into production in November/December of 1944.

Mauser stamped its magazines with a U to indicate that the magazine were not hardened. The U represents the German word ungehärtet and translates to unhardened.
This variation was stamped with P.38v over U on the left side of the magazine housing. No Mauser inspection stamp (E/WaA135) was stamped on the spine. The missing inspection stamp can indicate two things (1) the magazine was manufactured for the commercial market (police) or (2) the inspection stamp was simply omitted at the end of the war (production quantity became a priority at the end of the war instead of quality). This magazine variation can be found with Mauser pistols produced between approximately November 1944 and April 1945.