I actually have two of these old gems - one an older Helios-40 and one a newer Helios-40-2, both made in the Krasnogorsk Mechanical Plant (Krasnogorskij Mechanicheskij Zavod, or in Russian Красногорский Механический Завод). The older chrome-finished Helios-40 is actually an M39 mount with an M39-M42 adapter quasi-permanently fitted.