ZSh-3M helmet is a modernized version of the ZSh-3 shell. According to the ZSh-3M manual, the only difference between the M model and original helmet is the reduced distance between visor and shell in the upper position. However when I compared them side by side, there were a couple of visual differences. First of all, backing plate for the visor lowering mechanism became smaller in size. Second difference is the addition of the special metal plate that covered protruding screws that hold visor lowering button attached to the left pivoting axle.   ZSh-3M set; front view. Left view of the set showing visor lowering mechanism. Close up on the visor lowering mechanism. Note the reduced size of the backing plate and metal cover for the protruding screws. Back view of the set. Right view of the set. Close up on the right pivoting axle. Classic Mig fighter pilot setup. First developed around 1960, various ZSh-3 models were still produced as late as early 1990s, making it probably the most produced hard shell helmet in the world. Shown on this picture is ZSh-3M hard shell, ShL-78 leather flight helmet and KM-32 oxygen mask.