The 3M 6000-series is a general purpose (as opposed to military) respirator. It comes in 3 different configurations (with downward facing exhalation valve cover, without downward facing exhalation valve cover, and DIN-threaded connection w/o downward flowing exhalation valve cover) and 3 different sizes (small/medium/large).
The mask has 2 standard 3M bayonet connectors, one on each side of the mask. A filter or blanking plug must be installed on each connector. The mask can be optioned with a single DIN (40mm) connector at the front.
The mask harness is a simple 4-strap rubber affair, with a ladder-pattern at the back. 3M sells the straps, so if you break one you're not SOL. Everything on this mask has a spare or replacement part sold by 3M, so it is a very repairable mask.
Despite being a general purpose respirator series, certain models can filter out radioactive particles (to a degree) on such model would be the 3mm 6900 Full face gasmask. Which is being used by clean up crews at Fukushima. these models have a pink filter with a yellow siding and allow radioactive particles to be filtered. they also appear to be thicker than the regular filters usually used on this series.