The M10 was one of many Eastern European clones of the US M17 mask, and was issued to Czechoslovakian People's Army and East German's National People’s Army. After Cold War it was replaced in Czech by M90.
The Czechoslovakian M10 is heavily inspired by the US M17, but has many clear differences. The exhale system is different, having a metal housing with the exhale pointing directly outwards. Instead of the M17 style exhale, where the valve is covered by rubber and forced out through the bottom of the housing. The filter openings are larger and threaded. The head harness varies as the M10 head harness is made of a thicker grey elastic fabric with a rubber head pad and large rubber pull tabs. The M17's outserts have been found to fit with M10, but are noticeably smaller, and the filters are not interchangeable between the masks. Due to the different inhale sizes, and cap attachments. The M10 mask was used by both Czechoslovakia and East Germany. And remains in use today by the Czech Republic.
The M10M is an upgraded model which entered production in the late 1980s. Changes encompass the head harness, the voice diaphragm/exhale system. Which was changed to a large grey plastic piece, with a long "M1" style drinking tube wrapped around the assembly with a rubber flap folding over it.