In 1934 a new liner system for German helmets was adopted, namely the model 1931 liner. The new liner took into account the size of a soldier’s head rather than only the helmet shell
size. The M31 liner consists of two interlocking metal bands which are connected to each other with 5 steel leaf springs. The leather liner was attached to the inner metal band by small rivets made of aluminum and subsequently zinc-coated steel. The band is
stamped with the liner head size and appropriate shell size. The leather part consists of 8 separate «tongues» which are perforated with 5 stamped holes to allow for ventilation. The liners for larger helmets (size 68-70) have 9 leather tongues.
For precise adjustment for a soldier’s head size, a woven drawstring is inserted through a 6th hole on the tip of each tongue. Between the leather and the inner band, a wool
strip is attached to improve comfort and to avoid rubbing of the fragile leather against metal. Early liners were made mainly of aluminum parts changing to zinc-coated steel parts in 1940. The M31 liner consists of many parts and the 6 different liner
producers that that existed obtained certain components (leather and rivets) from several other manufacturers.