Finnish (US) M-9 Gas Mask, 23-120-1459 The M-61 is a Finnish gas mask manufactured by Nokia since the 1960s up to the 1980s. It was the standard issue gas mask for the Finnish Defense Forces, but was replaced by the updated M-95 in the 1990s. It is a side loading mask (meaning the filter attaches to the side) It uses 60 millimeter threads, but adapters are available to convert it to 40 millimeter threads. These masks are quite common on the surplus market, most filters (marked SUOD 61, suodatin is Finnish for filter) on the market have been checked by the Technical Depot of the Finnish Defence Forces in the 1970s-1980s. The weight in grams of the filter is written on the label as before the Gulf War it was thought that a properly stored filter would still be serviceable, providing the weight of the filter had not changed (which would indicate that the activated carbon had changed, taken up moisture etc.). The filters were manufactured by Kemira in Vaasa (now part of Scott Health & Safety, in turn part of Tyco International).