These filters fit 6000, 7000 series full face mask respirator we sell. The reason is that the extremely fine filtration traps all but the most minuscule particles. So our customers use them to protect against lead dusts in particular, as well as a host of other dusts, allergens and fumes. The filters are extremely light weight, flexible and they fit tight against the mask, all of which makes wearing this type of mask a bit more comfortable.