The Russian/Soviet Шлем Маска 66Му (ШМ-66Му) was the mask included with the Противогаз Мало Габаритный 2 (ПМГ-2) kit.  The Шлем Маска ШМ-66Му was an upgraded version of the Soviet ШМ-62, with a speech diaphragm and cut-out ear holes.  This example was made in Moscow in 1974.

Шлем Маска ШМ-66Му = "Helmet Mask ShM-66Mu"

Противогаз Малогабаритный = "Compact Gas Mask"